Exhibit
10.4

December  20,
2006

Martin Reidy
12 Via Fairallon
Orinda
CA 94563

Dear Martin,

This letter agreement
(this ‘‘Agreement’’)
memorializes our discussions and agreement concerning your continued
role with Digitas Inc. (the
‘‘Company’’) and its
subsidiaries as President, Modem Media, following the acquisition of
the Company by Publicis Groupe
(‘‘Publicis’’) pursuant to the Agreement
and Plan of Merger, dated December  20,  2006, by and among
the Company, Publicis, and Pacific Acquisition Corp., a wholly-owned
subsidiary of Publicis (the ‘‘Merger
Agreement’’).

1.    Retention
Bonus.    In consideration of your continued employment and your
agreement to the terms of Section 2 below, you will be eligible for a
special retention bonus of $1,105,611 (the
‘‘Retention Bonus’’). The
Retention Bonus shall be payable in two equal installments on each of
the first two anniversaries of the Acceptance Date (as defined in the
Merger Agreement), provided, in each case, that, subject to Section 3
below, you have remained continuously employed by the Company and its
subsidiaries through the applicable payment date.

2.    
Employment Agreement.    The Employment Agreement dated
January  21,  2005, between you and Modem Media, Inc. (the
‘‘Employment Agreement’’),
will remain in force and effect, and the Company acknowledges that the
Acceptance Date will constitute a Change in Control for purposes of the
Employment Agreement. Notwithstanding the foregoing, you and we agree
as follows:

•    Good
Reason.    Section 6(d)(i) of the Employment Agreement is
amended to provide that you shall be eligible to terminate employment
pursuant to such clause only (1) pursuant to the relocation trigger of
such clause, or (2) if, without your consent, and after a failure by
the Company to adequately cure within 10 business days of receipt of
written notice from you, either (a) your base pay is reduced, (b) your
bonus opportunity is materially diminished, or (c) your title or
position are materially diminished, it being understood and agreed that
any change to your position as a result of the Company no longer being
publicly traded or becoming a subsidiary as a result of the
transactions contemplated by the Merger Agreement or as a result of
changes to the organizational structure of the Company and its
subsidiaries as part of the integration with Publicis shall not give
you the right to terminate employment pursuant to such Section
6(d)(i).

•    Severance
Amount.    Section 6 of the Employment Agreement is amended to
provide that in the event that your employment terminates under
circumstances entitling you to severance benefits under Section 6(f) of
the Employment Agreement, you shall, in lieu of receiving the cash
severance provided for by Sections 6(e)(i), 6(e)(ii), and 6(f)(i) of
the Employment Agreement, receive (notwithstanding your termination of
employment) any unpaid installments of the Retention Bonus in a single
lump sum immediately upon your
termination.

•    Continuation Following
Second Anniversary of the Acceptance Date.    If you remain
employed by the Company and its affiliates following the second
anniversary of the Acceptance Date, the ‘‘Employment
Period’’ (as defined in the Agreement) shall continue
following such second anniversary; provided, however, that effective as
of such second anniversary, all provisions of the Employment Agreement
relating to a ‘‘Change in Control’’ shall
be deemed deleted, and it is hereby agreed and acknowledged that no
‘‘Change in Control’’ can be deemed to
occur under the Employment Agreement other than the occurrence of the
Acceptance Date.

3.    Death and
Disability.    Notwithstanding the foregoing, in the event of
your termination of employment prior to the second anniversary of the
Acceptance Date as a result of your death or Disability (as defined in
the Employment Agreement), you will receive (notwithstanding your
termination of employment) any unpaid installments of the Retention
Bonus in a single lump sum 










immediately upon your termination, and any
unvested stock options or restricted stock awarded to you prior to the
Acceptance Date will vest in full.

4.    Termination of
Merger Agreement.    In the event that the Merger Agreement is
terminated prior to the occurrence of an Acceptance Date, this
Agreement shall become null and void and of no
effect.

5.    Miscellaneous.    This Agreement
shall constitute a valid amendment of the Employment Agreement, and
shall be governed by the same dispute resolution provisions as the
Employment Agreement. Any payments made pursuant to this Agreement
shall be subject to applicable tax withholding. This Agreement may not
be amended or modified other than by a written agreement executed by
you, the Company, and Modem Media, Inc. (or your and their respective
successors and legal representatives).

Please indicate your
agreement with the foregoing by signing
below.


		Sincerely,





		/s/
Brian K. Roberts





		Digitas
Inc.





		/s/ Brian K.
Roberts





		Modem Media,
Inc.




Acknowledged and
Agreed:


/s/ Martin F.
Reidy