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                                                                 EXHIBIT 10.2(a)
 
                             STOCK OPTION AGREEMENT
 
     THIS STOCK OPTION AGREEMENT is made as of the 21st day of December, 1998,
between Caribiner International, Inc., a Delaware corporation (hereinafter
called the "Corporation"), and Christopher A. Sinclair, the Corporation's
President and Chief Executive Officer (hereinafter called the "Participant").
 
     WHEREAS, the Corporation desires to give the Participant an opportunity to
participate in the long-term growth of the Corporation by granting to the
Participant options to purchase the Corporation's common stock, par value $0.01
per share (the "Common Stock"), pursuant to the terms and conditions of this
Agreement.
 
     NOW, THEREFORE, in consideration of the mutual covenants hereinafter set
forth and for other good and valuable consideration, the receipt of which is
hereby acknowledged, the parties agree as follows:
 
          1. Grant of Option.  Subject to the ratification and approval by the
     stockholders of the Corporation, the Corporation hereby grants to the
     Participant the right and option (hereinafter called the "Option") to
     purchase an aggregate of up to Three Hundred Fifty Thousand (350,000)
     shares (the "Shares") of Common Stock (such number being subject to
     adjustment as provided in paragraph 7 hereof) on the terms and subject to
     the conditions herein set forth. Such Option shall vest and become
     exercisable as follows: (i) thirty-three and one-third percent (33 1/3%) of
     the Option herein granted (for up to One Hundred Sixteen Thousand Six
     Hundred Sixty-seven (116,667) shares) shall vest and may be exercised at
     any time on or after the first anniversary of this Agreement (unless
     terminated earlier pursuant to paragraph 6 hereof), (ii) thirty-three and
     one-third percent (33 1/3%) of the Option herein granted (for up to One
     Hundred Sixteen Thousand Six Hundred Sixty-seven (116,667) shares) shall
     vest and may be exercised on or after the second anniversary of this
     Agreement (unless terminated earlier pursuant to paragraph 6 hereof) and
     (iii) the remaining thirty-three and one-third percent (33 1/3%) of the
     Option herein granted (for up to One Hundred Sixteen Thousand Six Hundred
     Sixty-six (116,666) shares) shall vest and may be exercised on or after the
     third anniversary of this Agreement (unless terminated earlier pursuant to
     paragraph 6 hereof). The Option granted hereby is not intended to be an
     "incentive stock option" within the meaning of Section 422 of the Internal
     Revenue Code of 1986, as amended (the "Code"), and the Agreement shall be
     construed and interpreted in accordance with such intention.
 
          2. Exercise Price.  The exercise price of the Shares covered by the
     Option shall be the average of the high and low reported consolidated
     trading sales price of the Company's Common Stock as reported on the New
     York Stock Exchange on the date first set forth above, which is Eight
     Dollars and Fifty-six and One Quarter Cents ($8.5625) per Share.
 
          3. Term of Option.  Subject to paragraph 8 hereof, the Option granted
     hereby shall be exercisable in accordance with paragraph 1. The
     Participant's right to exercise the aforementioned Option shall expire ten
     (10) years from the date hereof (the "Expiration Date"). Unless terminated
     earlier pursuant to paragraph 6 hereof, the Option may not be exercised
     after the Expiration Date.
 
          4. Nontransferability.  The Option granted hereby shall not be
     transferable otherwise than by will or the laws of descent and
     distribution. More particularly (except as provided in the preceding
     sentence), the Option may not be sold, assigned, transferred, pledged,
     hypothecated or otherwise disposed of in any way, shall not be assignable
     by operation of law, and shall not be subject to execution, attachment or
     similar process. Any attempted sale, assignment, transfer, pledge,
     hypothecation or other disposition of the Option contrary to the provisions
     hereof, and the levy of any execution, attachment or similar process upon
     the Option, shall be null and void and without effect. The Option may be
     exercised by the Participant only during his lifetime or following his
     death pursuant to paragraph 6 hereof.
 
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          5. Disclosure and Risk.
 
          (a) The Participant represents and warrants to the Corporation as
     follows:
 
             (i) The Participant acknowledges that (A) neither the Option nor
        the Shares have been registered for resale under the Securities Act of
        1933, as amended (the "Securities Act"), and (B) the Corporation is
        under no obligation to effect the registration under the Securities Act
        of the Option and/or the Shares.
 
             (ii) The Shares will be acquired by the Participant for the
        Participant's own account, for investment and not with a view to, or for
        resale in connection with, any distribution or public offering thereof
        within the meaning of the Securities Act.
 
             (iii) The Corporation has made available to the Participant the
        opportunity to ask questions of the officers and management of the
        Corporation and to acquire information about the business and financial
        condition of the Corporation and has, and at the time of exercise of the
        Option will have, all information necessary for him to make an informed
        investment decision.
 
             (iv) He has received a copy of the Plan.
 
          (b) Each certificate representing the Shares will be endorsed with the
     following or a substantially similar legend:
 
             "THE SECURITIES EVIDENCED BY THIS CERTIFICATE HAVE NOT BEEN
        REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED (THE "SECURITIES
        ACT"), OR UNDER ANY APPLICABLE STATE SECURITIES LAWS, AND MAY NOT BE
        SOLD, TRANSFERRED, ASSIGNED, PLEDGED, HYPOTHECATED OR OTHERWISE DISPOSED
        OF UNLESS (i) THERE IS AN EFFECTIVE REGISTRATION STATEMENT UNDER THE
        SECURITIES ACT COVERING SUCH SECURITIES, OR (ii) THE CORPORATION
        RECEIVES A WRITTEN OPINION FROM COUNSEL FOR THE HOLDER OF THESE
        SECURITIES, REASONABLY SATISFACTORY TO THE CORPORATION, STATING THAT
        SUCH SALE, TRANSFER, ASSIGNMENT, PLEDGE, HYPOTHECATION OR OTHER
        DISPOSITION MAY BE MADE PURSUANT TO RULE 144 PROMULGATED UNDER THE
        SECURITIES ACT OR IS OTHERWISE EXEMPT FROM THE REGISTRATION AND
        PROSPECTUS DELIVERY REQUIREMENTS OF THE SECURITIES ACT AND APPLICABLE
        STATE SECURITIES LAWS."
 
          The Corporation need not allow a transfer of any of the Shares unless
     one of the conditions specified in the foregoing legend is satisfied. The
     Corporation may also instruct its transfer agent not to allow the transfer
     of any of the Shares unless one of the conditions specified in the
     foregoing legend is satisfied.
 
          Any legend endorsed on a certificate pursuant to the foregoing
     language and the stop transfer instructions with respect to such Shares
     shall be removed, and the Corporation shall promptly issue a certificate
     without such legend to the holder thereof if (i) the Shares are registered
     under the Securities Act and a prospectus meeting the requirements of
     Section 10 of the Securities Act is available and has been delivered or
     (ii) the holder provides the Corporation with a written opinion from
     counsel for such holder of the Shares, reasonably satisfactory to the
     Corporation, to the effect that a sale, transfer, assignment, pledge,
     hypothecation or other disposition of such Shares may be made without
     registration.
 
          6. Termination of Employment; Disability; Retirement; Death.
 
          (a) In the event that the Participant shall cease to be an employee of
     the Corporation for any reason other than death, Disability, Retirement,
     termination with or without Cause, or resignation for Good Reason (each as
     defined below), the Option may be exercised by the Participant (to the
     extent that the Participant shall have been entitled to do so as of the
     date of the termination of his employment with the Corporation) at any time
     prior to the Expiration Date of the Option or within 30 days after
     Participant shall so cease to be an employee of the Corporation, whichever
     is earlier. So long as the Participant shall continue to be an employee of
     the Corporation, the Option shall not be affected by any change of duties
     or position. The provisions of this Section 6(a) shall be subject to the
     provisions of Section 6(e) below.


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          (b) In the event of the Disability or Retirement of the Participant,
     the unexercised portion of the Option that is held by the Participant on
     the date of such Disability or Retirement, whether or not otherwise
     exercisable on such date, shall be exercisable one (1) year from the date
     of Disability or Retirement. "Disability" shall mean any termination of
     employment with the Corporation or a subsidiary because of a long-term or
     total disability, as determined by the Compensation Committee (the
     "Committee") of the Board of Directors (the "Board") of the Corporation in
     its sole discretion. "Retirement" shall mean a termination of employment
     with the Corporation or a subsidiary either (i) on a voluntary basis by a
     recipient who is at least 65 years of age or (ii) otherwise with the
     written consent of the Committee in its sole discretion.
 
          (c) During the lifetime of the Participant, the Option shall be
     exercisable only by him (or by his legal guardian or representative). In
     the event of the death of the Participant while he is an employee of the
     Corporation or any subsidiary, the Option (or unexercised portion thereof)
     which is held by the Participant at the date of death, whether or not
     exercisable on the date of death, shall be exercisable in accordance with
     the terms of this Agreement by the beneficiary designated by the
     Participant for such purpose (the "Designated Beneficiary") or if no
     Designated Beneficiary shall have been appointed or if the Designated
     Beneficiary shall predecease the Participant, by the Participant's personal
     representatives, heirs or legatees at any time for a period of one
     (1) year after the date of the Participant's death and any portion of the
     Option which is not exercised during such one (1) year period shall be
     forfeited.
 
          In the event of the death of the Participant following a termination
     of employment due to Retirement or Disability, if such death occurs before
     the Option (or any portion thereof) is exercised, the Option (or portion
     thereof) that is held by the Participant on the date of termination of
     employment, whether or not exercisable on such date, shall be exercisable
     by such Participant's Designated Beneficiary or if no Designated
     Beneficiary shall have been appointed or if the Designated Beneficiary
     shall predecease the Participant, by the Participant's personal
     representatives, heirs or legatees at any time for a period of one
     (1) year after the date of the Participant's death and any portion of the
     Option which is not exercised during such one (1) year period shall be
     forfeited.
 
          (d) In the event the Participant is terminated for Cause, the Option
     shall be exercisable by the Participant (to the extent that the Participant
     shall have been entitled to do so as of the date of the termination of his
     employment with the Corporation for Cause) at any time prior to the
     Expiration Date or within sixty (60) days after Participant's termination
     for Cause, whichever is earlier. "Cause" shall have the meaning set forth
     in Section 9(a) of that certain Employment Agreement by and between the
     Corporation and the Participant, dated as of December 21, 1998.
 
          (e) In the event the Participant is terminated without Cause or if
     Participant resigns for Good Reason, automatically upon any such
     termination or resignation, any unexercised portion of the Option shall
     immediately vest and become fully exercisable (without regard to the
     vesting provisions set forth in Paragraph 1 above), and the entire
     unexercised portion of the Option shall thereafter be exercisable (in whole
     or in part) at any time after such termination or resignation (as the case
     may be) prior to the Expiration Date, or for a period of two years after
     such termination or resignation (as the case may be), whichever is earlier.
     As used herein, the term "Good Reason" shall have the meaning set forth in
     Section 9(d) of that certain Employment Agreement by and between the
     Corporation and the Participant, dated as of December 21, 1998.
 
          7. Changes in Capital Structure.  If all or any portion of the Option
     shall be exercised subsequent to any stock dividend, stock split,
     recapitalization, merger, consolidation, combination or exchange of shares,
     separation, spin-off, reorganization, liquidation or the like occurring
     after the date hereof, as a result of which shares of any class shall be
     issued in respect of outstanding Common Stock or shares of Common Stock
     shall be changed into the same or a different number of shares of the same
     or another class or classes, the person or persons exercising the Option
     shall receive, for the aggregate price paid upon such exercise,
     the aggregate number and class of shares which, if the Shares (as
     authorized at the date hereof) had been purchased at the date hereof for
     the same aggregate price (on the basis of the price per share set forth in
 
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     paragraph 2 hereof) and had not been disposed of, such person or persons
     would be holding at the time of such exercise as a result of such purchase
     and all such share dividends, stock splits, recapitalizations, mergers,
     consolidations, combinations or exchanges of shares, separations,
     spin-offs, reorganizations, liquidations or the like; provided, however,
     that no fractional shares shall be issued upon any such exercise, and the
     aggregate price paid shall be appropriately reduced on account of any
     fractional share not issued. In no event shall any adjustments be made to
     the Option as a result of the issuance or redemption of securities of the
     Corporation for cash or other consideration, or upon the exercise of any
     conversion rights of any securities of the Corporation.
 
          8. Method of Exercising Option.  Subject to the terms and conditions
     of this Agreement, the Option may be exercised in whole or in part by
     giving written notice to the Secretary of the Corporation, at the address
     set forth below the Corporation's signature to this Agreement or such other
     location as may be designated by the Secretary of the Corporation. Such
     notice shall state the Participant's election to exercise the Option and
     the number of Shares in respect of which it is being exercised, and shall
     be signed by the person or persons so exercising the Option. Payment for
     the Shares may be made (i) in cash or (ii) at the option of the Committee,
     or, in absence of the Committee, the Board, by delivery of Common Stock
     already owned by the Participant and having an aggregate Market Price (as
     defined in the Plan) on the date of such delivery equal to the aggregate
     exercise price of the shares so purchased or (iii) at the option of the
     Committee, or, in absence of the Committee, the Board, by delivery of a
     combination of cash and Common Stock having an aggregate Market Price on
     the date of such delivery equal to the aggregate exercise price of the
     shares so purchased. The Corporation shall deliver a certificate or
     certificates representing the shares of Common Stock so purchased as soon
     as practicable after the notice of election has been received. In the event
     the Option shall be exercised by any person or persons other than the
     Participant, the notice of election shall be accompanied by appropriate
     proof of the right of such person or persons to exercise the Option. All
     shares of Common Stock that shall be purchased upon the exercise of the
     Option as provided herein shall be fully paid and nonassessable.
 
          9. Change of Control.
 
          (a) As long as Participant is an employee of the Corporation, a
     "Change of Control" of the Corporation shall cause the Option (or the
     unexercised portion thereof), whether or not currently exercisable, to
     become immediately exercisable, in whole or in part, as of the effective
     date of such Change of Control without regard to any vesting provisions or
     condition precedent which may be contained in paragraph 1 of this
     Agreement. For purposes of this paragraph, a "Change of Control" shall be
     deemed to have occurred if (i) any person or "group" (other than Warburg,
     Pincus Investors, L.P. or any affiliate thereof) acquires, in a single
     transaction or series of related transactions, 50% or more of the
     outstanding Common Stock; (ii) during any period of two consecutive years,
     individuals that at the beginning of such period constitute the Board cease
     for any reason to constitute a majority thereof, unless the election, or
     the nomination for election by the stockholders, of each such new director
     was approved by a vote of at least two-thirds of the directors then still
     in office which were directors at the beginning of the period; or
     (iii) the sale of all or substantially all of the assets of the Corporation
     (other than to a wholly-owned subsidiary of the Corporation).
 
          (b) Notwithstanding the provisions of paragraph 9(a), in the case that
     the Corporation is merged or consolidated with another corporation, or the
     assets or stock of the Corporation is acquired by another corporation, or a
     separation, reorganization or liquidation of the Corporation occurs, the
     Board, or the Board of Directors of any corporation assuming the
     obligations of the Corporation hereunder, shall make appropriate provisions
     for the protection of the Option by substitution on an equitable basis of
     appropriate stock of the Corporation, or appropriate stock of the merged,
     consolidated or otherwise reorganized corporation, provided that only the
     excess of the aggregate Market Price of the shares subject to the Option
     immediately after such substitution over the aggregate exercise price
     thereof is not less than the excess of the aggregate Market Price of the
     shares subject to the Option immediately before such substitution over the
     aggregate exercise price thereof.
 
 
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          10. Optionee Not a Stockholder.  The Participant shall not have any
     rights as a stockholder with respect to any shares of Common Stock subject
     to the Option prior to the date on which he is recorded as the holder of
     such shares on the records of the Corporation.
 
          11. Taxes.  The Corporation may make such provisions and take such
     steps as it may deem necessary or appropriate for the withholding of all
     federal, state, local and other taxes required by law to be withheld with
     respect to the Option including, but not limited to (i) reducing the number
     of shares of Common Stock otherwise deliverable, based upon their fair
     market value on the date of exercise, to permit deduction of the amount of
     any such withholding taxes from the amount otherwise payable under this
     Agreement; (ii) deducting the amount of any such withholding taxes from any
     other amount then or thereafter payable to the Participant; or
     (iii) requiring the Participant, Designated Beneficiary or legal
     representative to pay to the Corporation the amount required or desirable
     to enable it to satisfy its withholding obligations as a condition of
     releasing the Common Stock.
 
          12. General Provisions.
 
          (a) The Corporation shall at all times during the term of the Option
     reserve and keep available such number of Shares as will be sufficient to
     satisfy the requirements of this Option Agreement, shall pay all fees and
     expenses necessarily incurred by the Corporation in connection therewith,
     and shall use its best efforts to comply with all laws and regulations
     which, in the reasonable opinion of counsel to the Corporation, are
     applicable thereto.
 
          (b) This Agreement shall be governed by and construed in accordance
     with the laws of the State of New York without regard to principles of
     conflicts of laws.
 
          (c) Any notice to be given hereunder by either party to the other
     shall be in writing and shall be given either by personal delivery,
     facsimile or by mail, registered or certified, postage prepaid, return
     receipt requested, or by overnight delivery addressed to the other party at
     the respective addresses or facsimile numbers set forth below their
     signatures to this Agreement, or at any other address or facsimile number
     as such party may hereafter specify in writing.
 
          (d) No amendments or modifications to this Agreement shall be binding
     unless made in writing and signed by the parties hereto.
 
          (e) The waiver by either party of a breach of any term or provision of
     this Agreement shall not operate or be construed as a waiver of a
     subsequent breach of the same provision or of the breach of any other term
     or provision of this Agreement.
 
          (f) As used herein, the masculine gender shall include the feminine
     and the neuter genders, the neuter shall include the masculine and the
     feminine genders, the singular shall include the plural, and the plural
     shall include the singular.
 
          (g) The headings in this Agreement are solely for convenience of
     reference and shall be given no effect in the construction or
     interpretation of this Agreement.
 
          (h) The invalidity or enforceability of any provision of this
     Agreement shall not affect the validity or enforceability of any other
     provision of this Agreement, which shall remain in full force and effect.
 
          (i) NEITHER THE PLAN NOR THIS AGREEMENT SHALL BE (1) CONSTRUED AS
     GIVING THE PARTICIPANT THE RIGHT TO BE RETAINED IN THE EMPLOY OF THE
     CORPORATION OR ANY SUBSIDIARY THEREOF OR TO BE ENTITLED TO ANY REMUNERATION
     OR BENEFITS NOT SET FORTH IN THE PLAN OR THIS AGREEMENT OR (2) INTERFERE
     WITH OR LIMIT THE RIGHT OF THE CORPORATION OR ANY SUBSIDIARY THEREOF TO
     MODIFY THE TERMS OF OR TERMINATE THE PARTICIPANT'S EMPLOYMENT AT ANY TIME
     WITH OR WITHOUT CAUSE.
 
          13. Incorporation by Reference.  Reference is hereby made to the
     Corporation's 1996 Stock Option Plan, as amended as of February 27, 1998
     (the "Plan"). Although it is expressly understood and agreed that

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     the Options granted herein are not subject to the Plan, the following
     provisions of the Plan are hereby incorporated herein by reference and
     shall be deemed to be a part hereof as is set forth fully herein:
     Article 3 (Administration) of the Plan; Section 5.6 (Exercise and Payment)
     of the Plan; Section 5.8 (Rights as a Stockholder) of the Plan;
     Section 5.9 (General Restrictions) of the Plan; Article 6
     (Nontransferability of Options) of the Plan; Section 7.6 (Leave of Absence)
     of the Plan; Article 8 (Adjustment Upon Changes in Capitalization) of the
     Plan and Article 11 (Miscellaneous Provisions) of the Plan. In the event
     the Plan is terminated for any reason whatsoever, notwithstanding such
     termination, the foregoing provisions shall remain applicable to the terms
     and conditions of the Options herein granted as if such Plan had not been
     terminated.
 
     IN WITNESS WHEREOF, the parties have caused this Agreement to be duly
executed as of the day and year first above written.
 
                                        PARTICIPANT
                                              /s/ CHRISTOPHER A. SINCLAIR
                                        --------------------------------------
                                         Name:    Christopher A. Sinclair
                                         Address:
                                         Facsimile:
 
                                        CARIBINER INTERNATIONAL, INC.

                                        By:          /s/ ERROL M. COOK
                                            ----------------------------------
                                            Address:   16 West 61st Street
                                                       New York, New York 10023
                                            Facsimile: (212) 541-5384