<PAGE>
 
                          INMC MORTGAGE HOLDINGS, INC.
                           1998 STOCK INCENTIVE PLAN



     1.   Purpose of Plan.  The purpose of this 1998 Stock Incentive Plan
          ---------------                                                
("Plan") of INMC Mortgage Holdings, Inc. (d.b.a. IndyMac Mortgage Holdings,
Inc.), formerly known as CWM Mortgage Holdings, Inc., a Delaware corporation
(the "Company"), is to enable the Company, IndyMac, Inc. ("IndyMac") and any of
their respective subsidiaries or affiliates to attract, retain and motivate
their employees, consultants, agents, officers and directors by providing
incentives related to equity interests in and the financial performance of the
Company.

     2.   Persons Eligible Under Plan.  Any person, including any director of
          ---------------------------                                        
the Company or IndyMac, who is an officer or employee of the Company, IndyMac,
or any of their respective subsidiaries or affiliates or an individual who
performs services for the Company, IndyMac, or any of their respective
subsidiaries or affiliates of a nature similar to those performed by officers or
employees, such as consultants and agents, and any non-employee director of
IndyMac who is not also a member of the Board (as hereinafter defined) (any of
the foregoing, an "Employee") shall be eligible to be considered for the grant
of an Award (as defined in Section 5 below) or Awards under Section 5 of this
Plan.  No member of the Board of Directors of the Company (the "Board") who is
not an officer or employee of the Company, IndyMac, or any of their respective
subsidiaries or affiliates (a "Non-Employee Director") shall be eligible to
receive any Awards under this Plan, except for nonqualified stock options
granted automatically under the provisions of Section 10 of this Plan ("Director
Options").

     3.   Stock Subject to Plan.
          --------------------- 

          (a) ISO Limit.  The maximum number of Common Shares, $0.01 par value
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     per share, of the Company (the "Common Shares") that may be issued pursuant
     to options intended to qualify as incentive stock options ("Incentive Stock
     Options") under Section 422 of the Internal Revenue Code of 1986, as
     amended (the "Code"), granted under this Plan is 6,000,000, and provided
     further that, except as otherwise provided herein, the aggregate Fair
     Market Value (as defined in Section 10) of Common Shares with respect to
     which options intended to qualify as Incentive Stock Options are
     exercisable for the first time by any individual during any calendar year
     shall not exceed the limit, if any, set forth in Section 422(d) of the Code
     or any successor provision thereto.  For purposes of this subsection (a),
     the Fair Market Value (as defined in Section 10) of any Common Shares shall
     be determined as of the time the Incentive Stock Option with respect to the
     Common Shares is granted.  Pursuant to Section 422(a)(2) of the Code, only
     employees (as that term is used in Section 422(a)(2) of the Code) of the
     Company or the Company's wholly-owned subsidiaries may receive options
     intended to qualify as Incentive Stock Options under this Plan.

                                       1
<PAGE>
 
          (b) Aggregate/Individual Share Limit.
              -------------------------------- 


               (i) The maximum number of Common Shares that may be issued
          pursuant to all Awards (including Incentive Stock Options, as set
          forth in subsection (a) above) granted under this Plan, other than
          Common Shares that are issued pursuant to Awards and subsequently
          reacquired by the Company pursuant to the terms and conditions of such
          Awards ("Reacquired Common Shares"), is 6,000,000, subject to
          adjustment as provided in or pursuant to Section 6 or 10 hereof (such
          maximum number, as so adjusted, shall be referred to as the "Share
          Limit").

               (ii) Notwithstanding anything contained herein to the contrary,
          the aggregate number of Common Shares subject to options, stock
          appreciation rights, and awards of restricted stock granted during any
          calendar year to any individual shall be limited to 500,000.


          (c) Share Reservation.  No Award may be granted under this Plan
              -----------------                                          
     unless, on the date of grant, the sum of (i) the maximum number of Common
     Shares issuable at any time pursuant to such Award, plus (ii) the number of
     Common Shares that have previously been issued pursuant to Awards granted
     under this Plan, other than Reacquired Common Shares available for reissue,
     plus (iii) the maximum number of Common Shares that may be issued at any
     time after such date of grant pursuant to Awards that are outstanding on
     such date, does not exceed the Share Limit.  Common Shares distributed
     under the Plan may be treasury shares, authorized but unissued shares or
     shares purchased in the open market for this purpose.

          (d) Reissue of Awards and Common Shares.  Awards payable in cash or
              -----------------------------------                            
     Common Shares that are forfeited or for any reason are not so paid under
     this Plan, as well as Common Shares subject to Awards that expire or for
     any reason are terminated and are not issued or constitute Reacquired
     Common Shares, shall again be available for subsequent Awards under the
     Plan.

          (e) Fractional Shares/Minimum Issue.  Fractional share interests shall
              -------------------------------                                   
     be disregarded, but may be accumulated.  No fewer than 100 Common Shares
     may be purchased on exercise of any option granted under this Plan
     ("Option") at one time unless the number purchased is the total number at
     the time available for purchase under the Option.

          (f) Privileges of Stock Ownership.  Except as otherwise expressly
              -----------------------------                                
     authorized by this Plan, an Award recipient shall not be entitled to any
     privilege of stock ownership as to any Common Shares subject to an Option
     granted under this Plan prior to the satisfaction of all conditions to the
     valid exercise of the Option.

                                       2
<PAGE>
 
     4.   Administration of Plan.
          ---------------------- 

          (a) The Committee.  Except for the provisions of Section 10 (which to
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     the maximum extent feasible shall be self-effectuating), this Plan shall be
     administered by a committee of the Board (the "Committee") consisting of
     two or more directors, each of whom is a "Non-Employee Director," as such
     term is defined in Rule 16b-3 under the Securities Exchange Act of 1934, as
     amended (the "Exchange Act"), and an "Outside Director," as such term is
     defined for purposes of Section 162(m) of the Code.

          (b) Powers of the Committee.  Subject to the express provisions of
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     this Plan, the Committee shall be authorized and empowered to do all things
     necessary or desirable in connection with the administration of this Plan
     including, without limitation, the following:

                (i)  adopt, amend and rescind rules and regulations relating to
          this Plan;

                (ii) determine which persons meet the requirements of Section 2
          hereof for eligibility under this Plan and to which of such eligible
          persons, if any, Awards will be granted hereunder;

               (iii) grant Awards to eligible persons and determine the terms
          and conditions thereof, including, but not limited to, the number of
          Common Shares issuable pursuant thereto, the time not more than ten
          (10) years after the date of an Award at which time the Award shall
          expire or (if not vested) terminate, and the conditions upon which
          Awards become exercisable or vest or shall expire or terminate, and
          the consideration, if any, to be paid upon receipt, exercise or
          vesting of Awards;

               (iv) determine whether, and the extent to which, adjustments are
          required pursuant to Section 6 hereof;

               (v)  interpret and construe this Plan and the terms and
          conditions of any Award granted under Section 5, whether before or
          after the date set forth in Section 7; and

               (vi) determine the circumstances under which, consistent with the
          provisions of Section 7, any outstanding Award under Section 5 may be
          amended;

     which authority (except as to clauses (ii) and (iii) above) shall remain in
     effect so long as any Award remains outstanding under this Plan.

          (c) Specific Committee Responsibility and Discretion Regarding Awards.
              -----------------------------------------------------------------
     Subject to the express provisions of this Plan, the Committee, in its sole
     and absolute discretion, shall determine all of the terms and conditions of
     each Award granted under 

                                       3
<PAGE>
 
Section 5 of this Plan, which terms and conditions may include, subject to such
limitations as the Committee may from time to time impose, among other things,
provisions that:

               (i)  permit the recipient of such Award, including any recipient
          who is a director or officer of the Company, to pay the purchase price
          of the Common Shares or other property issuable pursuant to such
          Award, or such recipient's tax withholding obligation upon such
          issuance or in respect of such Award or Shares, in whole or in part,
          by any one or more of the following:

                    (A)  the delivery of previously owned shares of capital
               stock of the Company (including shares acquired as or pursuant to
               Awards) then having been owned by the recipient for at least six
               (6) months (or such other period required under applicable law)
               or the delivery of other property, or

                    (B)  the delivery of a promissory note, under any applicable
               financing plan or on such other terms and conditions, as in
               either case authorized by the Committee, consistent with
               applicable law;

               (ii)  accelerate the receipt of benefits pursuant to such Award
          upon the occurrence of specified events, including, without
          limitation, a change of control of the Company, an acquisition of a
          specified percentage of the voting power of the Company, the
          dissolution or liquidation of the Company, a sale of substantially all
          of the property and assets of the Company or an event of the type
          described in Section 6 hereof, or pursuant to the provisions of an
          employment contract not inconsistent with the terms of this Plan, or
          in other circumstances or upon the occurrence of other events as
          deemed appropriate by the Committee;

               (iii) qualify such Award as an Incentive Stock Option;

               (iv)  extend the exercisability or term of any or all such
          outstanding Awards, change the price of any or all such outstanding
          Awards or otherwise change previously imposed terms and conditions, in
          the specified events described in clause (ii) above or in other
          circumstances or upon the occurrence of other events as deemed
          appropriate by the Committee, in each case subject to Section 7;

                (v)  authorize the conversion, succession or substitution of
          outstanding Awards under Section 5 upon the occurrence of any event of
          the type described in Section 6, or in other circumstances or upon the
          occurrence of other events as deemed appropriate by the Committee;
          and/or

               (vi)  provide for automatic grants of Awards or successive
          Awards.

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<PAGE>
 
          (d) Binding Determinations.  Any action taken by, or inaction of, the
              ----------------------                                           
     Company, the Board or the Committee relating or pursuant to this Plan shall
     be within the absolute discretion of that entity or body and shall be
     conclusive and binding upon all persons.  No member of the Board or officer
     of the Company shall be liable for any such action or inaction of the
     entity or body, of another person or, except in circumstances involving bad
     faith, of himself or herself.

          (e) Reliance on Experts.  In making any determination or in taking or
              -------------------                                              
     not taking any action under this Plan, the Board and the Committee may
     obtain and may rely upon the advice of experts, including professional
     advisors to the Company.  No director, officer or agent of the Company
     shall be liable for any such action or determination taken or made or
     omitted in good faith.

          (f) Delegation.  The Committee may delegate ministerial, non-
              ----------                                              
     discretionary functions to individuals who are officers or employees of the
     Company.  The Committee also may delegate to certain officer(s) of the
     Company (i) the authority to grant Awards pursuant to Section 5 of the
     Plan, provided that such delegation is set forth in writing and includes
           --------                                                          
     all applicable limitations and parameters to such Awards, and provided
                                                                   --------
     further that such Awards are subsequently ratified by the Committee; and
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     (ii) with respect to unvested Awards that are Incentive Stock Options that
     have been granted to an employee of the Company (other than an employee who
     is subject to Section 16 of the Exchange Act), the authority to accelerate
     the exercisability of such Incentive Stock Options to allow them to be
     exercised within the three-month period commencing upon the date that the
     employee's employment by the Company terminates by reason of the transfer
     of such employee to employment by IndyMac, provided, however, that to the
                                                --------  -------             
     extent (A) such accelerated Options are not exercised prior to the
     expiration of such three-month period, or (B) the acceleration of the
     exercisability of such Options causes such Options to fail to satisfy the
     requirements of Section 422(d) of the Code, such Options shall
     automatically be converted into non-qualified Options and shall continue to
     be exercisable in accordance with their terms (as accelerated Options)
     until they expire or otherwise terminate under the terms of the Plan.

     5.   Awards.
          ------ 

          (a) Types of Awards.  The Committee, on behalf of the Company, is
              ---------------                                              
     authorized under this Plan to enter into any type of arrangement with an
     Employee that is not inconsistent with the provisions of this Plan and that
     by its terms, involves or might involve the issuance of (i) Common Shares,
     (ii) an option, warrant, convertible security, stock appreciation right or
     similar right with an exercise or conversion privilege at a fixed or
     variable price related to the Common Shares or other equity securities of
     the Company and/or the passage of time, the occurrence of one or more
     events, or the satisfaction of performance criteria or other conditions, or
     any combination of these variables, or any similar security contemplated by
     subsection (b) below, or (iii) any similar security with a value derived
     from the value of the Common Shares or other equity securities of the

                                       5
<PAGE>
 
     Company, all of which may or may not involve the payment of cash
     consideration, subject to subsection (e) below.  The authorization of any
     such arrangement (including any benefits described in Section 5(e)) is
     referred to herein as the grant of an "Award".  The date of grant may be at
     or after (but not before) the date the Committee authorizes the Award.  All
     Awards shall be evidenced by a writing with a schedule memorializing the
     grant of the Award to the recipient and setting forth certain specifics
     with respect to the terms and conditions of the Award ("Award Memorandum").

          (b) Form of Awards.  Awards are not restricted to any specified form
              --------------                                                  
     or structure and may include, without limitation, sales or bonuses of
     stock, restricted stock, performance restricted stock, stock options,
     reload stock options, stock purchase warrants, other rights to acquire
     stock, securities convertible into or redeemable for stock, stock
     appreciation rights, limited stock appreciation rights, phantom stock,
     dividend equivalents, performance units or performance shares, and an Award
     may consist of one such security or benefit, or two or more of them in any
     combination or alternative.  In addition, any Award that is intended to
     qualify as an Incentive Stock Option will automatically be converted into a
     non-qualified stock option to the extent that such Award does not satisfy
     any applicable requirement under Section 422 of the Code.

          (c) Restricted Stock Awards.  If expressly provided by the Committee,
              -----------------------                                          
     and without limiting subsection (b) above, Awards of restricted Common
     Shares ("Restricted Stock") may be made to the holder of any Option, based
     upon dividends or distributions that would have been received had the
     Common Shares covered by the Option been issued and outstanding on the
     applicable dividend record date.  The terms and conditions of any such
     Awards of Restricted Stock shall be specified in the applicable Award
     Memorandum.

          (d) Time and Method of Exercise. Awards may be exercised in whole or
              ---------------------------                                     
     in part at such time or times as shall be determined by the Committee and
     set forth in the applicable Award Memorandum.  Awards shall be exercised in
     accordance with procedures established by the Committee, subject to Section
     4(c)(i) and any holding periods required under applicable law.

          (e) Price; Consideration; Option Pricing Limit.  Common Shares may be
              ------------------------------------------                       
     issued pursuant to an Award for any lawful consideration as determined by
     the Committee, including, without limitation, cash, Common Shares (valued
     at then Fair Market Value, as defined in Section 10), or services rendered
     by the recipient of such Award; provided that no Common Shares shall be
                                     --------                               
     issued for less than the minimum lawful consideration and no Option which
     is intended to be an Incentive Stock Option shall be granted with an
     exercise price that is less than the Fair Market Value (as defined in
     Section 10) of the underlying Common Shares on the date of grant.

          (f) Effect of Termination of Service or Death; Change in Subsidiary
              ---------------------------------------------------------------
     Status.  Subject to Section 4(c)(ii), each Option and all other rights
     ------                                                                
     thereunder, to the extent not 

                                       6
<PAGE>
 
     exercised (whether or not presently exercisable), shall terminate and
     become null and void at such time as the holder of such Option terminates
     service as an Employee, except that

               (i) if the holder terminates service as an Employee for a reason
          other than cause (as determined by the Committee in its sole
          discretion), death or permanent and total disability (as defined in
          clause (ii) below), the holder may at any time within a period of
          three months after such termination exercise such Option to the extent
          such Option was exercisable on the date of such termination;

               (ii) if the holder terminates service as an Employee by reason of
          permanent and total disability (within the meaning of Section 22(e)(3)
          of the Code), or if the holder becomes permanently and totally
          disabled within three months after termination described in clause
          (i), the holder may at any time within a period of twelve (12) months
          after such termination exercise such Option to the extent such Option
          was exercisable on the date of such termination; and

               (iii) if the holder terminates service as an Employee by reason
          of death, or within three months after a termination described in
          clauses (i) or (ii), then such Option may be exercised within a period
          of twelve (12) months after the holder's termination of service as an
          Employee, to the extent such Option was exercisable on the date of
          such termination;

     provided, however, that in no event may any such Option be exercised by any
     --------  -------                                                          
     holder after its expiration date.

          Notwithstanding any of the foregoing provisions of this subsection
     (f), if the holder of an Option is an Employee of IndyMac or one of its
     subsidiaries or affiliates and IndyMac or the Employee ceases to provide
     services to the Company, or if the holder of an Option is an Employee of an
     entity which is a subsidiary or affiliate of the Company or IndyMac and
     such entity ceases to be such a subsidiary or affiliate, such event shall
     be deemed for purposes of this subsection (f) to be a termination of the
     holder's service as an Employee described in clause (i) above.  Absence
     from work caused by military service or authorized sick leave shall not be
     considered a termination of service as an Employee for purposes of this
     subsection (f).

          (g) Cash Awards; Loans.  The Committee shall have the express
              ------------------                                       
     authority to create, add or include a cash payment or benefit under this
     Plan, whether in lieu of, in addition to or as an Award or as a component
     of another type of Award, and to make or authorize loans to finance, or to
     otherwise accommodate the financing, acquisition or exercise of an Award or
     the satisfaction of any related tax liability.

          (h) Transfer Restrictions.  Unless otherwise permitted in the
              ---------------------                                    
     applicable Award Memorandum pursuant to the discretion of the Committee, no
     Award granted hereunder 

                                       7
<PAGE>
 
     shall be transferable other than by will or the laws of descent and
     distribution or pursuant to a qualified domestic relations order.

          (i) Tax Withholding.  Upon the issuance of Common Shares, the payment
              ---------------                                                  
     of cash or any other taxable event in respect of an Award under this Plan,
     such number of shares or amount of cash or other consideration, as the case
     may be, otherwise issuable or payable may be reduced by the amount
     necessary to satisfy the minimum applicable tax withholding requirements
     imposed on the Company, IndyMac or any of their respective subsidiaries or
     affiliates in respect of such Award or event, all to the extent and in such
     manner as the Committee may determine.

     6.   Adjustments and Acceleration.
          ---------------------------- 

          (a) Adjustments.  If (i) the outstanding securities of the class then
              -----------                                                      
          subject to this Plan (the "outstanding shares") (A) are increased,
          decreased, exchanged or converted as a result of a stock split
          (including a split in the form of a stock dividend), reverse stock
          split, recapitalization, or similar event or (B) are exchanged for or
          converted into cash, property or a different number or kind of
          securities (or if cash, property or securities are distributed in
          respect of the outstanding shares), as a result of a reorganization,
          merger, consolidation, exchange, recapitalization, restructuring or
          reclassification, or (ii) substantially all of the property and assets
          of the Company are sold as an entirety, or (iii) the Company is
          liquidated and dissolved, then, the Committee (or, in the case of
          Director Options, the Board) shall, in such manner and to such extent
          (if any) as is equitable and appropriate, make proportionate
          adjustments in (x) the number and type of shares or other securities
          or cash or other property that may be acquired pursuant to Options and
          other Awards previously granted under this Plan (and, where
          applicable, the exercise price thereof so as to maintain the same
          aggregate exercise price), (y) the maximum number and type of shares
          or other securities, cash, or property that may be issued or delivered
          pursuant to Options (including Incentive Stock Options and Director
          Options) and other Awards thereafter granted under this Plan, and (z)
          such other terms as necessarily are affected by such event.  In the
          case of an extraordinary distribution, merger, reorganization,
          consolidation, combination, sale of assets, exchange or spin off, the
          Committee (or the Board, in the case of Director Options) may make
          provisions for a substitution or exchange of any or all outstanding
          Options or other Awards or rights (or for the securities, cash or
          property deliverable upon exercise of such outstanding Options or
          other Awards or rights), based upon the distribution or consideration
          payable to holders of the Common Shares of the Company upon or in
          respect of such event.

                                       8
<PAGE>
 
          (b)  Acceleration.
               ------------ 

               (i)  A "Change in Control" for purposes of this Plan shall mean
          the occurrence of any one of the following events:

                    (A) An acquisition (other than directly from the Company) of
               any common stock or other "Voting Securities" (as hereinafter
               defined) of the Company by any "Person" (as the term person is
               used for purposes of Sections 13(d) or 14(d) of the Exchange Act,
               immediately after which such Person has "Beneficial Ownership"
               (within the meaning of Rule 13d-3 under the Exchange Act) of
               twenty five percent (25%) or more of the then outstanding shares
               of the Company's common stock or the combined voting power of the
               Company's then outstanding Voting Securities; provided, however,
                                                             --------  ------- 
               that in determining whether a Change in Control has occurred,
               Voting Securities which are acquired in a "Non-Control
               Acquisition" (as hereinafter defined) shall not constitute an
               acquisition which would cause a Change in Control.  For purposes
               of this Plan, (1) "Voting Securities" shall mean the Company's
               outstanding voting securities entitled to vote generally in the
               election of directors and (2) a "Non-Control Acquisition" shall
               mean an acquisition by (a) an employee benefit plan (or a trust
               forming a part thereof) maintained by (x) the Company, (y)
               IndyMac or, (z) any corporation or other Person of which a
               majority of its voting power or its voting equity securities or
               equity interest is owned, directly or indirectly, by the Company
               (for purposes of this definition, a "Subsidiary"), (b) the
               Company or any of its Subsidiaries, or (c) any Person in
               connection with a "Non-Control Transaction" (as hereinafter
               defined);

                    (B)  The individuals who as of January 27, 1998 are members
               of the Board (the "Incumbent Board") cease for any reason to
               constitute at least two-thirds of the members of the Board;
                                                                          
               provided, however, that if the election, or nomination for
               --------  -------                                         
               election by the Company's common stockholders, of any new
               director was approved by a vote of at least two-thirds of the
               Incumbent Board, such new director shall, for purposes of this
               Plan, be considered as a member of the Incumbent Board; provided
                                                                       --------
               further, however, that no individual shall be considered a member
               -------  -------                                                 
               of the Incumbent Board if such individual initially assumed
               office as a result of either an actual or threatened "Election
               Contest" (as described in Rule 14a-11 under the Exchange Act) or
               other actual or threatened solicitation of proxies or consents by
               or on behalf of a Person other than the Board (a "Proxy Contest")
               including by reason of any agreement intended to avoid or settle
               any Election Contest or Proxy Contest; or

                                       9
<PAGE>
 
                    (C)  The consummation of: (1) A merger, consolidation or
                         reorganization involving the Company, unless such
                         merger, consolidation or reorganization is a "Non-
                         Control Transaction."  A "Non-Control Transaction"
                         shall mean a merger, consolidation or reorganization of
                         the Company where: (a) the stockholders of the Company,
                         immediately before such merger, consolidation or
                         reorganization, own directly or indirectly immediately
                         following such merger, consolidation or reorganization,
                         at least seventy percent (70%) of the combined voting
                         power of the outstanding Voting Securities of the
                         corporation resulting from such merger, consolidation
                         or reorganization (the "Surviving Corporation") in
                         substantially the same proportion as their ownership of
                         the Voting Securities immediately before such merger,
                         consolidation or reorganization; (b) the individuals
                         who were members of the Incumbent Board immediately
                         prior to the execution of the agreement providing for
                         such merger, consolidation or reorganization constitute
                         at least two-thirds of the members of the board of
                         directors of the Surviving Corporation, or in the event
                         that, immediately following the consummation of such
                         transaction, a corporation beneficially owns, directly
                         or indirectly, a majority of the Voting Securities of
                         the Surviving Corporation, the board of directors of
                         such corporation; and (c) no Person other than (w) the
                         Company, (x) any Subsidiary, (y) any employee benefit
                         plan (or any trust forming a part thereof) maintained
                         by the Company, IndyMac, the Surviving Corporation, or
                         any Subsidiary, or (z) any Person who, immediately
                         prior to such merger, consolidation or reorganization
                         had Beneficial Ownership of twenty-five percent (25%)
                         or more of the then outstanding Voting Securities or
                         common stock of the Company, has Beneficial Ownership
                         of twenty-five percent (25%) or more of the combined
                         voting power of the Surviving Corporation's then
                         outstanding Voting Securities or its common stock;

                         (2)  A complete liquidation or dissolution of the
                         Company, or

                         (3)  The sale or other disposition of all or
                         substantially all of the assets of the Company to any
                         Person (other than a transfer to a Subsidiary).

                                       10
<PAGE>
 
               Notwithstanding the foregoing provisions of this Section 6(b)(i),
          a Change in Control shall not be deemed to occur solely because any
          Person (the "Subject Person") acquired Beneficial Ownership of more
          than the permitted amount of the then outstanding common stock or
          Voting Securities as a result of the acquisition of common stock or
          Voting Securities by the Company which, by reducing the number of
          shares of common stock or Voting Securities then outstanding,
          increases the proportional number of shares Beneficially Owned by the
          Subject Persons; provided, however, that if a Change in Control would
                           --------  -------                                   
          occur (but for the operation of this sentence) as a result of the
          acquisition of common stock or Voting Securities by the Company, and
          after such share acquisition by the Company, the Subject Person
          becomes the Beneficial Owner of any additional common stock or Voting
          Securities which increases the percentage of the then outstanding
          common stock or Voting Securities Beneficially Owned by the Subject
          Person, then a Change in Control shall occur.

               (ii)  Except as otherwise provided in Section 10(j), prior to a
          Change in Control, the Committee may determine in respect of Awards
          held by Employees that upon or in anticipation of the occurrence of
          the Change in Control benefits under Awards shall be accelerated only
          for a limited period of time, which period of time shall not be less
          than a period of time reasonably necessary to realize the benefits of
          such acceleration nor more than one year after the Change in Control.
          If such a determination is not made, then (subject to the last
          sentence of this clause) upon the occurrence of a Change in Control
          and without further action by the Board or the Committee, (A) each
          Option and stock appreciation right shall become immediately
          exercisable, (B) performance Restricted Stock shall immediately vest
          free of restrictions, and (C) each performance share Award shall
          become payable to the Employee.  The Committee may override the
          limitations on acceleration in this Section 6(b)(ii) by express
          provision in the Award Memorandum or otherwise, and may accord any
          holder of an Award a right to refuse any acceleration, whether
          pursuant to the Award Memorandum or otherwise, in such circumstances
          as the Committee may approve.  Any acceleration of Awards shall comply
          with any applicable regulatory and financial accounting requirements,
          including without limitation Section 422 of the Code.

               (iii)  Any Awards that are (or but for a holder's rejection of
          acceleration would have been) accelerated under this Section 6 and
          that are not exercised or vested prior to a dissolution of the Company
          or a reorganization event described in Section 6(a) that the Company
          does not survive shall terminate, provided that if provision has been
                                            --------                           
          made, consistent with the terms hereof, for the substitution, exchange
          or other settlement of Awards, such Awards shall be substituted,
          exchanged or otherwise settled in accordance with such provision.

               (iv) Any Awards that are (or but for the holder's rejection of
          the acceleration would have been) accelerated that are not exercised
          or vested prior to 

                                       11
<PAGE>
 
          an abandonment or termination of a transaction subject to shareholder
          approval that triggered the Change in Control (as evidenced by public
          announcement, Board resolution, execution of documents terminating the
          transaction, or other action or document objectively confirming such
          abandonment or termination), shall be restored to their prior status
          (except for the effects of the passage of time) as if no Change in
          Control had occurred.

     7.    Amendment and Termination of Plan.
           --------------------------------- 
 
           (a)    No Award shall be granted under this Plan after January 27,
     2008.  Although Common Shares may be issued after January 27, 2008 pursuant
     to Awards granted prior to such date, no Common Shares otherwise shall be
     issued under this Plan after such date.  Notwithstanding the foregoing, any
     Award granted prior to such date may vest or be amended after such date in
     any manner that would have been permitted prior to such date, except that
     (except as provided herein) no such amendment shall increase the number of
     shares subject to or comprising such Award, or extend the final expiration
     date of the Award or reduce (below the Fair Market Value (as defined in
     Section 10) on the date of the amendment) the exercise price of or under
     such Award.

          (b)     The Board may, without shareholder approval, at any time and
     from time to time, suspend, discontinue or amend this Plan in any respect
     whatsoever, except that no such amendment shall impair any rights under any
     Award theretofore made under the Plan without the consent of the holder of
     such Award. Furthermore, and except as and to the extent otherwise
     permitted by the provisions hereof, no such amendment shall, without
     shareholder approval, cause the Plan to cease to satisfy any applicable
     condition of Rule 16b-3 under the Exchange Act or cause any Award under the
     Plan to cease to qualify for any applicable exception under Section 162(m)
     of the Code.

     8.   Effective Date of Plan: Shareholder Approval.  This Plan shall be
          --------------------------------------------                     
effective as of January 27, 1998, the date upon which it was approved by the
Board; provided, however, that no Common Shares may be issued under this Plan
       --------  -------                                                     
until it has been approved by the affirmative votes of the holders of a majority
of the Common Shares of the Company present, or represented, and entitled to
vote at a meeting duly held in accordance with applicable law.

                                       12
<PAGE>
 
     9.   Legal Issues.
          ------------ 

          (a) Compliance and Choice of Law: Severability.  This Plan, the
              ------------------------------------------                 
     granting and vesting of Awards under this Plan and the issuance and
     delivery of Common Shares and/or the payment of money under this Plan or
     under Awards granted hereunder are subject to compliance with all
     applicable federal and state laws, rules and regulations (including but not
     limited to state and federal securities law and federal margin
     requirements) and to such approvals by any listing, regulatory or
     governmental authority as may, in the opinion of counsel for the Company,
     be necessary or advisable in connection therewith.  Any securities
     delivered under this Plan shall be subject to such restrictions as the
     Company may deem necessary or desirable to assure compliance with all
     applicable legal requirements.  This Plan, the Awards, all documents
     evidencing Awards and all other related documents shall be governed by, and
     construed in accordance with, the laws of the State of Delaware.  If any
     provision shall be held by a court of competent jurisdiction to be invalid
     and unenforceable, the remaining provisions of this Plan (subject to
     Section 9(b)) shall continue in effect.


          (b) Plan Construction.  It is the intent of the Company that this Plan
              -----------------                                                 
     and Awards hereunder satisfy and be interpreted in a manner that in the
     case of recipients who are or may become persons subject to Section 16 of
     the Exchange Act satisfies the applicable requirements of Rule 16b-3 under
     the Exchange Act so that such persons will be entitled to the benefits of
     Rule 16b-3 or other exemptive rules under Section 16 of the Exchange Act
     and will not be subjected to avoidable liability thereunder.  If any
     provision of this Plan or of any Award would otherwise frustrate or
     conflict with the intent expressed above, that provision to the extent
     possible shall be interpreted and deemed amended so as to avoid such
     conflict, but to the extent of any remaining irreconcilable conflict with
     such intent as to such persons in the circumstances, such provision shall
     be deemed inoperative.


          (c)  REIT Qualification.
               ------------------ 

               (i)  It is the intent of the Company that this Plan and Awards
          hereunder satisfy and be interpreted in a manner consistent with the
          Company's continued status as a "qualified real estate investment
          trust" under the Code.  If any provision of this Plan or any Award
          would otherwise frustrate or conflict with the intent expressed above,
          that provision to the extent possible shall be interpreted and deemed
          amended so as to avoid such conflict, but to the extent of any
          remaining irreconcilable conflict with such intent as to the Company,
          such provision shall be deemed inoperative.

               (ii)  Notwithstanding anything contained herein to the contrary,
          no participant may receive any Common Shares upon the grant, exercise
          or vesting of an option or right or other Award to the extent it will
          cause such person to beneficially or constructively own equity shares
          in excess of 9.8% of the equity 

                                       13
<PAGE>
 
          shares of the Company. In the event that a participant would be
          otherwise entitled to claim or seek to exercise any right which upon
          delivery of Common Shares would cause such participant to beneficially
          or constructively own equity shares in excess of the ownership limit,
          the Company shall have the right, notwithstanding any option or right
          previously granted to the participant, to deliver a check or cash to
          the participant in lieu thereof.

          (d) Non-Exclusivity of Plan.  Nothing in this Plan shall limit or be
              -----------------------                                         
     deemed to limit the authority of the Board or the Committee to grant awards
     or authorize any other compensation, with or without reference to the
     Common Shares, under any other plan or authority.

     10.  Non-Employee Director Options
          -----------------------------

          (a) Participation.  Awards relating to the Common Shares authorized
              -------------                                                  
     under this Plan shall be made under this Section 10 only to Non-Employee
     Directors.

          (b) Certain Definitions.  The following definitions shall apply to
              -------------------                                           
     this Section 10:

               (i) "Business Day" shall mean any day, other than Saturday,
          Sunday or any statutory holiday in the state of California.

               (ii) "Director Option" shall mean an Option granted to a Non-
          Employee Director pursuant to this Section 10.

               (iii) "Disability" shall mean a "permanent and total disability"
          within the meaning of Section 22(e)(3) of the Code.

               (iv)  "Fair Market Value" on a specified date shall mean (A) if
          the Common Shares are listed or admitted to trade on a national
          securities exchange, the average of the high and low reported sales
          prices of the Common Shares on the Composite Tape on such date, as
          published in the Western Edition of The Wall Street Journal, on the
          principal national securities exchange on which the Common Shares are
          so listed or admitted to trade, or, if there is no trading of the
          Shares on such date, then the average of the high and low reported
          sales prices of the Common Shares as quoted on such Composite Tape on
          the next preceding date on which there was trading in such Shares; (B)
          if the Common Shares are not listed or admitted to trade on a national
          securities exchange, the average of the high and low reported prices
          for the Common Shares on such date, as furnished by the National
          Association of Securities Dealers, Inc. ("NASD") through the NASDAQ
          National Market Reporting System (or a similar organization, if the
          NASD is no longer reporting such information); (C) if the Common
          Shares are not listed or admitted to trade on a national securities
          exchange and are not 

                                       14
<PAGE>
 
          reported on the National Market Reporting System, the arithmetic mean
          between the bid and asked prices for the Shares on such date, as
          furnished by the NASD or a similar organization; or (D) if the Common
          Shares are not listed or admitted to trade on a national securities
          exchange nor reported on the National Market Reporting System and if
          bid and asked prices for the stock are not furnished by the NASD or a
          similar organization, the value as established by the Board at such
          time for purposes of this Plan.

               (v) "Retirement" shall mean retirement or resignation as a
          director after at least five (5) years service as a director.

          (c) Annual Awards.  On the first Business Day in June in each calendar
              -------------                                                     
     year during the term of the Plan, commencing in June 1998, there shall be
     granted automatically (without any action by the Committee or the Board) a
     nonqualified stock option (the grant date of which shall be such date in
     June) to each Non-Employee Director then in office to purchase the number
     of Common Shares equal to 30,000 multiplied by a fraction, the numerator of
     which is the earnings per Common Share (on a fully diluted basis, excluding
     the one time charge to earnings resulting from the acquisition by the
     Company of its manager in June 1997) of the Company for the fiscal year of
     the Company ended immediately before the date of grant of the Non-Employee
     Director option (as reported in the audited Financial Statements included
     in the Company's Annual report on Form 10-K filed with the Securities and
     Exchange Commission ("SEC"), but in no event less than zero) (the "EPS
     Numerator Amount") and the denominator of which is (i) in 1998, $1.51; and
     (ii) in each year after 1998, the greater of (A) $1.79 compounded at a rate
     of 15% per year (i.e., in 1999, $2.06; in 2000, $2.37; in 2001, $2.72; in
     2002, $3.13), or (B) the EPS Numerator Amount for the fiscal year of the
     Company ended immediately before the fiscal year used in determining the
     EPS Numerator Amount.  The number 30,000 and the specific dollar amounts
     herein are subject to adjustment in those events set forth in subsection
     (h) below.  The formula contained in this Section 10(c) may be amended by
     subsequent action of the Board to provide either for an alternative formula
     for calculating the number of Common Shares to be awarded annually, or to
     provide for the annual award of a fixed number of Common Shares; provided
                                                                      --------
     that, in either case, (i) the number of Common Shares to be awarded
     ----                                                               
     annually to Non-Employee Directors under such alternative formula or fixed
     number is no greater than that provided for under the formula set forth
     herein, and (ii) each Non-Employee Director receives the same number of
     Common Shares as every other Non-Employee Director under such alternative
     formula or fixed number.

          (d) Maximum and Minimum Number of Shares.  Notwithstanding anything to
              ------------------------------------                              
     the contrary contained herein, a Non-Employee Director shall not receive
     Options for less than 20,000 nor more than 50,000 Common Shares pursuant to
     this Section 10 in any year.

                                       15
<PAGE>
 
          (e) Purchase Price.  The exercise price for Shares under each Non-
              --------------                                               
     Employee Director option shall be equal to 100% of the Fair Market Value of
     a Common Share on the date the Director Option is granted.  The exercise
     price of any option granted under this Section 10 shall be paid in full at
     the time of each purchase in cash equivalent or in Common Shares valued at
     their Fair Market Value on the date of exercise of such option, or partly
     in such shares and partly in cash, provided that any such Common Shares
                                        -------- ----                       
     used in payment shall have been owned by the Non-Employee Director at least
     six months prior to the date of exercise.

          (f) Option Period and Exercisability.  Each Director Option granted
              --------------------------------                               
     under this Section 10 shall become fully exercisable, in whole or in part,
     on the first anniversary of the grant date.  Each option granted under this
     Section 10 and all rights or obligations thereunder shall expire on the
     earlier of the tenth anniversary of the date of grant or the liquidation or
     dissolution of the Company and shall be subject to earlier termination as
     provided below.

          (g) Termination of Directorship.  If a Non-Employee Director's
              ---------------------------                               
     services as a member of the Board terminate by reason of death, Disability
     or Retirement, an option granted pursuant to this Section 10 then held by
     such Non-Employee Director shall immediately become and shall remain
     exercisable for one year after the date of such termination or until the
     expiration of the stated term of such option, whichever first occurs.  If a
     Non-Employee Director's services as a member of the Board terminate for any
     other reason (other than Cause), any option granted pursuant to this
     Section 10 which is not then exercisable shall terminate and any such
     option which is then exercisable may be exercised for three months after
     the date of such termination or until the expiration of the stated term,
     which ever first occurs.  If a Non-Employee Director is terminated for
     Cause, all Director Options granted to such Non-Employee Director shall be
     forfeited and shall no longer be exercisable, effective on the date of such
     termination for Cause.  For purposes of this Section 10, "Cause" shall
     mean, with respect to any Non-Employee Director, termination on account of
     any act of (i) fraud or intentional misrepresentation, (ii) embezzlement,
     misappropriation or conversion of assets or opportunities of the Company or
     any affiliate, or (iii) conviction of a felony.

          (h) Adjustments.  The provisions of this Section 10 and Director
              -----------                                                 
     Options granted hereunder shall be subject to Section 6.  If there shall
     occur any event described in Section 6(a), then in addition to the matters
     contemplated thereby, the Board shall, in such manner and to such extent
     (if any) as is appropriate and equitable, proportionately adjust the dollar
     amounts set forth elsewhere in this Section 10.


          (i) Loans.  Subject to the requirements of applicable law, the Board
              -----                                                           
     may authorize loans to Non-Employee Directors to finance the exercise of
     Awards; provided, however, that no loan shall be made to any Non-Employee
             --------  -------                                                
     Director to finance the exercise of an Award made under this Section 10
     unless (i) such loan is made pursuant to a full recourse promissory note,
     and (ii) such loan, if secured by Common Shares 

                                       16
<PAGE>
 
     (whether issuable under the Award in question or otherwise), is made in
     compliance with Regulation G of the Federal Reserve Board.

          (j) Acceleration Upon a Change in Control.  Upon the occurrence of a
              -------------------------------------                           
     Change in Control referred to in Section 6(b), each Director Option granted
     under this Section 10 shall become immediately exercisable in full subject
     to the terms thereof (other than with respect to the Committee's
     discretion).  To the extent that any Director Option granted under this
     Section 10 is not exercised prior to (i) a dissolution of the Company or
     (ii) a merger or other corporate event that the Company does not survive,
     and no provision is (or consistent with the provisions of Section 9 or 10
     can be) made for the assumption, conversion, substitution or exchange of
     the option, the Director Option shall terminate upon the occurrence of such
     event.

          (k) Other Provisions.  The provisions of Sections 3(e)-(f), 5(h) and 7
              ----------------                                                  
     through 9 are incorporated herein by this reference.

                                       17
<PAGE>
 
                 AMENDMENT TO THE 1998 STOCK INCENTIVE PLAN OF
                        INDYMAC MORTGAGE HOLDINGS, INC.
             (Adopted by the Board of Directors on July 21, 1998)

     The 1998 Stock Incentive Plan of IndyMac Mortgage Holdings, Inc. is hereby
amended to revise Section 10(b)(iv) so that, as amended, Section 10(b)(iv) shall
read as follows:

               "Fair Market Value" on a specified date shall mean (A) if the
          Common Shares are listed or admitted to trade on a national securities
          exchange, the average of the average of the high and low reported
          sales prices of the Common Shares on the Composite Tape, as published
          in the Western Edition of The Wall Street Journal, on the ten days
          preceding such date on which the Common Shares trade on such principal
          national securities exchange; (B) if the Common Shares are not listed
          or admitted to trade on a national securities exchange, the average of
          the average of the high and low reported prices for the Common Shares
          on the ten days preceding such date on which such prices for the
          Common Shares are furnished by the National Association of Securities
          Dealers, Inc. ("NASD") through the NASDAQ National Market Reporting
          System (or a similar organization, if the NASD is no longer reporting
          such information); (C) if the Common Shares are not listed or admitted
          on a national securities exchange and are not reported on the National
          Market Reporting System, the arithmetic mean of the arithmetic mean
          between the bid and asked prices for the Common Shares on the ten days
          preceding such date on which bid and asked prices for the Common
          Shares are furnished by the NASD or a similar organization; or (D) if
          the Common Shares are not listed or admitted to trade on a national
          securities exchange nor reported on the National Reporting System, and
          if bid and asked prices for the Common Shares are not furnished by the
          NASD or a similar organization, the value as established by the Board
          at such time for purposes of this Plan."

                                       18
<PAGE>
 
                 AMENDMENTS TO THE 1998 STOCK INCENTIVE PLAN OF
                        INDYMAC MORTGAGE HOLDINGS, INC.
            (Adopted by the Board of Directors on January 20, 1999)

     (1)
          The 1998 Stock Incentive Plan of IndyMac Mortgage Holdings, Inc. is
     hereby amended to revise Section 10(b)(iv) so that, as amended, Section
     10(b)(iv) shall read as follows:



               "Fair Market Value" on a specified date shall mean (A) if the
          Common Shares are listed or admitted to trade on a national securities
          exchange, the average of the high and low reported sales prices of the
          Common Shares on the Composite Tape on such date, as published in the
          Western Edition of The Wall Street Journal, on the principal national
          securities exchange on which the Common Shares are so listed or
          admitted to trade, or, if there is no trading of the Shares on such
          date, then the average of the high and low reported sales prices of
          the Common Shares as quoted on such Composite Tape on the next
          preceding date on which there is trading in such Shares; (B) if the
          Common Shares are not listed or admitted to trade on a national
          securities exchange, the average of the high and low reported prices
          for the Common Shares on such date, as furnished by the National
          Association of Securities Dealers, Inc. ("NASD") through the NASDAQ
          National Market Reporting System (or a similar organization, if the
          NASD is no longer reporting such information); (C) if the Common
          Shares are not listed or admitted to trade on a national securities
          exchange and are not reported on the National Market Reporting System,
          the arithmetic mean between the bid and asked prices for the Shares on
          such date, as furnished by the NASD or a similar organization; or (D)
          if the Common Shares are not listed or admitted to trade on a national
          securities exchange nor reported on the National Market Reporting
          System and if bid and asked prices for the stock are not furnished by
          the NASD or a similar organization, the value as established by the
          Board at such time for purposes of this Plan."

                                       19
<PAGE>
 
                 AMENDMENTS TO THE 1998 STOCK INCENTIVE PLAN OF
                        INDYMAC MORTGAGE HOLDINGS, INC.
            (Adopted by the Board of Directors on January 20, 1999)


     (2)
          The 1998 Stock Incentive Plan of IndyMac Mortgage Holdings, Inc. is
     hereby amended to revise Section 10(e) so that, as amended, Section 10(e)
     shall read as follows:



               "The exercise price for Shares under any Director Option shall be
          equal to 100% of the Fair Market Value of a Common Share on the date
          the Director Option is granted.  The exercise price for Shares under
          any Director Option may be modified by a separate vote of the members
          of the Board who are officers of the Company, as well as the full
          Board; provided, that the modified exercise price shall be no less
          than 100% of the Fair Market Value of a Common Share on the date the
          exercise price of the Director Option is modified.  The exercise price
          of any option granted under this Section 10 shall be paid in full at
          the time of each purchase in cash equivalent or in Common Shares
          valued at their Fair Market Value on the date of exercise of such
          option, or partly in such shares and partly in cash, provided that any
                                                               -------- ----    
          such Common Shares used in payment shall have been owned by the Non-
          Employees Director at least six months prior to the date of exercise."

                                       20
<PAGE>
 
                 AMENDMENT TO THE 1998 STOCK INCENTIVE PLAN OF
                        INDYMAC MORTGAGE HOLDINGS, INC.
             (Adopted by the Board of Directors on March 1, 1999)



     The 1998 Stock Incentive Plan of IndyMac Mortgage Holdings, Inc. is hereby
amended to add the following sentence to the end of Section 10(c) of the 1998
Plan:
 

               "Notwithstanding the foregoing, beginning with calendar year 1999
          and for each calendar year thereafter during the term of the Plan, the
          annual award of stock options to Non-Employee Directors shall be on
          the same date as the annual grant of Awards to Employees pursuant to
          this Plan."

                                       21