<PAGE>
                                   AMENDMENT
                                     TO THE
                              REINSURANCE AGREEMENT

                                      AMONG

Capitol Indemnity Corporation (hereinafter referred to as the "Company") and
Darwin National Assurance Company (hereinafter referred to as "Reinsurer").

WHEREAS, the parties desire to modify certain terms and conditions of the
Reinsurance Agreement between the parties dated July 1, 2004;

NOW, THEREFORE, for the consideration mentioned and other good and valuable
consideration, the receipt and sufficiency of which is hereby acknowledged, the
parties do agree as follows:

1.    Article VII is hereby amended in its entirety as follows:

      A.    The Company shall pay to the Reinsurer:

            100% of the written premium charged and collected by the Company in
            connection with the Policies referenced in Article I (A) (ii), net
            of any other outside reinsurance purchased on this subject premium,
            plus 100% of the unearned premium charged and collected by the
            Company in connection with the Policies referenced in Article I (A)
            (i), net of any other outside reinsurance purchased on this subject
            premium.

      The reinsurance premiums set forth above shall be subject to a commission
      allowance payable to the Company in an amount equal to the compensation
      paid by the Company to Darwin Professional Underwriters, Inc. in relation
      to such business. The Reinsurer shall also compensate the Company as set
      forth below:

                  1.    Ceding Commission

                        The Company will be paid a ceding commission (as a
                        percentage of gross written premiums in respect of
                        business that is produced by Darwin Professional
                        Underwriters, Inc. (hereinafter referred to as "DPUI")
                        and for which Policies are issued by the Company)
                        according to the following schedule:
<TABLE>
<S>                                                             <C>
Policies' premium written on the books of the Company
   in calendar year 2006                                        0.5%
Policies' premium written on the books of the Company
</TABLE>

<PAGE>

<TABLE>
<S>                                                             <C>
   in calendar year 2007                                        1.0%
Policies' premium written on the books of the Company
   in calendar year 2008                                        2.0%
Policies' premium written on the books of the Company
   in calendar year 2009 and thereafter                         3.0%;
</TABLE>

                        provided, that in the event of an IPO, the ceding
                        commission will increase to 3.0% of the premium written
                        on the books of the Company effective as of January 1 of
                        the year following the year in which the IPO takes
                        place; provided, further, that in the event of a sale by
                        Alleghany Insurance Holdings, LLC (hereinafter referred
                        to as "AIHL") of securities representing a majority of
                        the voting power in DPUI (determined on an as-converted
                        basis) and/or Reinsurer to an insurance company or an
                        insurance holding company (a "Strategic Sale"), or in
                        the event of a sale by AIHL of securities to financial
                        investors (i.e., investors which are not insurance
                        companies or insurance holding companies) which would
                        cause AIHL's voting interest in DPUI (determined on an
                        as-converted basis) and/or Reinsurer to drop below 35%
                        (a "Financial Sale"), the ceding commission will
                        increase to 3.0% upon the closing of such Strategic Sale
                        or Financial Sale. For the purposes of this Article VII,
                        an "IPO" means the initial public offering of common
                        stock of DPUI or Reinsurer pursuant an effective
                        registration statement under the Securities Act of 1933,
                        as amended, in connection with which the common stock of
                        DPUI or Reinsurer becomes listed on a U.S. national
                        securities exchange or traded on the Nasdaq National
                        Market System.

                  2.    Reimbursement of Expenses

                        In addition to payment of the ceding commission provided
                        for above, direct expenses incurred by the Company
                        arising from the issuance of policies of the Company in
                        respect of business produced by DPUI will be reimbursed
                        by Reinsurer to Company as follows:

<PAGE>

<TABLE>
<CAPTION>
EXPENSE                             ALLOCATION OF METHODOLOGY
---------------------------------   -------------------------------------------
<S>                                 <C>
Taxes/Boards/                       Reinsurer responsible for all taxes,
Bureaus                             boards and bureaus related to Policies.

Fines/Penalties                     Reinsurer responsible for all fines and
                                    penalties arising out of acts, errors
                                    or omissions of Reinsurer or its
                                    affiliates and/or related to the Policies.

Assessments                         Reinsurer responsible for all assessments
                                    (including, but not limited to, premium
                                    and loss based) to the extent they arise
                                    from or relate to Policies.

Market Conduct Exam Fees            Reinsurer responsible for exam fees
                                    related to regulatory review of DPUI
                                    produced business and/or the
                                    reinsurance/underwriting management
                                    agreements implementing the
                                    Company/DPUI/Reinsurer relationship.

Corporate Outside Counsel Fees      Reinsurer responsible for all
corporate Incurred by the Company   outside counsel legal fees and expenses
(Company/DPUI/                      incurred by the Company in connection
Reinsurance Transactions)           with regulatory matters related to
                                    Company/DPUI/Reinsurer transactions.
                                    The Company shall obtain Reinsurer's
                                    prior approval before incurring such
                                    legal fees in excess of $2,000 for any
                                    individual matter and such approval shall
                                    not be unreasonably withheld by Reinsurer.
</TABLE>

2.    Article VIII is hereby amended in its entirety as follows:

      A.    The Company shall furnish the Reinsurer with all necessary data
            respecting losses for as long as one of the parties hereto has a
            claim against the other arising from this Agreement.

      B.    Within 15 days of the end of any month the Reinsurer shall furnish
            the Company with a report of reinsurance premium, commission

<PAGE>

            allowance and ceding commission due. Any balances shown to be due
            will be remitted with said report.

      C.    Payment by the Reinsurer of its proportion of loss, Allocated Loss
            Adjustment Expenses and reimbursable expenses paid by the Company
            shall be made by the Reinsurer to the Company within 15 days after
            proof of payment is received by the Reinsurer.

3.    Article XV is hereby amended in its entirety as follows:

      A.    It is agreed that when the Company files with an insurance
            department or establishes reserves for claims covered and unearned
            premium hereunder, as required by law, the Company shall forward to
            the Reinsurer a statement showing the proportion of such loss,
            Allocated Loss Adjustment Expense and unearned premium reserves
            which is applicable to the Reinsurer. In the event that the Company
            is not permitted by any insurance regulator to take full and
            complete credit on its financial statements for this reinsurance and
            that the collateral provided by the Reinsurer in Article XV B. below
            shall not be satisfactory with an insurance regulator to take full
            and complete credit in its financial statements for this
            reinsurance, then, the Reinsurer hereby agrees to apply for and
            secure delivery to the Company of a clean, irrevocable and
            unconditional Letter of Credit , that is issued , and presentable
            and payable in the United States, by a bank or trust company, that
            is a member of the Federal Reserve System, and is in a format
            acceptable to the governmental authority having jurisdiction over
            the Company's reserves, in an amount equal to the Reinsurer's
            proportion of such loss (including case and incurred but not
            reported), Allocated Loss Adjustment Expenses (including case and
            incurred but not reported), unearned premium and commission
            reserves. The Letter of Credit will be issued for a period of not
            less than one year, and will be automatically extended for one year
            from its date of expiration or any future expiration date unless 60
            days prior to any expiration date the issuing bank notifies the
            Company by registered mail that the issuing bank elects not to
            consider the Letter of Credit extended for any additional period, in
            which case the Reinsurer shall deliver to the Company a replacement
            Letter of Credit on or prior to such expiration date. In lieu of the
            Letter of Credit described above, the Reinsurer may provide the
            Company other collateral (such as cash advances, trust agreements,
            escrow accounts, or a combination of the foregoing) acceptable to
            the Company and to the governmental authority having jurisdiction
            over the Company's reserves.

            The Company and the Reinsurer agree that the Letter of Credit or
            other collateral provided by the Reinsurer under this provision may
            be drawn upon at any time, notwithstanding any other provisions in
            this

<PAGE>

            Agreement by the Company, including any liquidator, rehabilitator,
            receiver or conservator of the Company, for the following purposes:

            1)    to reimburse the Company for the Reinsurer's share of the
                  Ultimate Net Losses paid by the Company and which has not
                  otherwise been paid by the Reinsurer;

            2)    to reimburse the Company for the Reinsurer's share of premium
                  and commission returned under Policies reinsured under this
                  Agreement on account of cancellation of such Policies and
                  which has not otherwise been paid by the Reinsurer;

            3)    to fund an account with the Company in an amount at least
                  equal to the deduction, for reinsurance ceded, from the
                  Company's liabilities for amounts ceded under this Agreement.
                  Such cash deposits shall be held in an interest bearing
                  account separate from the Company's other assets, and interest
                  thereon shall accrue to the benefit of the Reinsurer. Such
                  amount shall include, but not be limited to, amounts for
                  reserves for claims and losses incurred, including losses
                  incurred but not reported, loss adjustment expenses, and
                  unearned premiums;

            4)    to reimburse the Company for the Reinsurer's share of
                  surrenders and benefits or losses paid by the Company under
                  the terms and provisions of the Policies reinsured under this
                  Agreement; and

            5)    to pay any other amounts the Company claims are due under this
                  Agreement.

      B. In addition to any collateralization required as set forth in (A)
      above, upon the earliest to occur of (i) an IPO, (ii) a Strategic Sale or
      (iii) a Financial Sale (a "Collateralization Event"), all obligations of
      the Reinsurer to the Company (gross of any outside third party reinsurance
      which may be applicable), including but not limited to obligations related
      to the Ultimate Net Loss, loss reserves (case and incurred but not
      reported), unearned premium reserves and allocated loss adjustment expense
      reserves related to the Policies reinsured hereunder, must be fully
      collateralized pursuant to arrangements reasonably satisfactory to the
      Company. Such collateralization may, at Company's direction, include the
      provision by Reinsurer to Company of a clean, irrevocable and
      unconditional Letter of Credit having the same terms and which may be
      drawn upon for the same reasons as previously set forth above in this
      Article XV. The amount which must be fully collateralized in the event of
      a Collateralization Event will be recalculated every three (3) months
      following the occurrence of the Collateralization Event. In the event
      that, following a Collateralization Event, the actuaries for the Company
      and the actuaries for the Reinsurer disagree as to the appropriate level
      of reserves to be established in respect of such obligations of the
      Reinsurer, then the obligations of the Reinsurer will be collateralized at
      the level specified by the Company's actuaries, or in the event of
      disagreement between the

<PAGE>

      Reinsurer and the Company, the Reinsurer and the Company will mutually
      agree upon a nationally recognized independent actuarial firm to conduct
      an actuarial study of the obligations of the Reinsurer to the Company, the
      fees and expenses of which will be paid by the Reinsurer, and the
      obligations of the Reinsurer to the Company will be collateralized at the
      level specified by such third independent actuarial firm.

4.    This Amendment may be executed in counterparts of like form, each of
      which, when executed, shall be deemed together an original and all of
      which taken together shall constitute one and the same instrument.

5.    Except as hereby amended, the terms and provisions of the Agreement shall
      remain in full force and effect.

6.    The parties hereby agree that the effective date for this Amendment shall
      be January 1, 2006.

Darwin National Assurance Company        Capitol Indemnity Corporation

By:   /s/ John L. Sennott, Jr.           By:   /s/ David Pauly
      ------------------------------           ----------------------------

Name: John L. Sennott, Jr.               Name: David Pauly

Title: CFO                               Title: CEO