UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549

                                  -------------

                                  SCHEDULE 13D
                                 (Rule 13d-101)

             INFORMATION TO BE INCLUDED IN STATEMENTS FILED PURSUANT
            TO RULE 13d-1(a) AND AMENDMENTS THERETO FILED PURSUANT TO
                                  RULE 13d-2(a)

                    Under the Securities Exchange Act of 1934
                                (Amendment No.4)*



                             Fair Isaac Corporation
--------------------------------------------------------------------------------
                                (Name of Issuer)

                                  Common Stock
--------------------------------------------------------------------------------
                         (Title of Class of Securities)

                                    303250104
--------------------------------------------------------------------------------
                                 (CUSIP Number)

                         Sandell Asset Management Corp.
                               40 West 57th Street
                                   26th Floor
                               New York, NY 10019
                   Attention: Richard Gashler, General Counsel
                                  212-603-5700

                                 With a Copy to:
                              Marc Weingarten, Esq.
                            Schulte Roth & Zabel LLP
                                919 Third Avenue
                               New York, NY 10019
                                  212-756-2000
--------------------------------------------------------------------------------
(Name, Address and Telephone Number of Person Authorized to Receive Notices and
                                 Communications)

                                  July 24, 2009
                               ------------------
             (Date of Event which Requires Filing of this Statement)

If the filing person has previously filed a statement on Schedule 13G to report
the acquisition that is the subject of this Schedule 13D, and is filing this
schedule because of Rule 13d-1(e), 13d-1(f) or 13d-1(g), check the following box
[ ].

Note: Schedules filed in paper format shall include a signed original and five
copies of the schedule, including all exhibits. See Rule 13d-7 for other parties
to whom copies are to be sent.

                          (Continued on following pages)
                               (Page 1 of 9 Pages)

--------------------
* The remainder of this cover page shall be filled out for a reporting person's
initial filing on this form with respect to the subject class of securities, and
for any subsequent amendment containing information which would alter
disclosures provided in a prior cover page. The information required on the
remainder of this cover page shall not be deemed to be "filed" for the purpose
of Section 18 of the Securities Exchange Act of 1934 ("Act") or otherwise
subject to the liabilities of that section of the Act but shall be subject to
all other provisions of the Act (however, see the Notes).



----------------------------                        ----------------------------
CUSIP No.  303250104            SCHEDULE 13D        Page 2 of 9 Pages
----------------------------                        ----------------------------

------------- -----------------------------------------------------------------
     1        NAME OF REPORTING PERSON

              Castlerigg Master Investments Ltd.
------------- -----------------------------------------------------------------
     2        CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (a) |_|  (b) |_|
------------- -----------------------------------------------------------------
     3        SEC USE ONLY
------------- -----------------------------------------------------------------
     4        SOURCE OF FUNDS

              WC
------------- -----------------------------------------------------------------
     5        CHECK IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT
              TO ITEMS 2(d) or 2(e)     |_|
------------- -----------------------------------------------------------------
     6        CITIZENSHIP OR PLACE OF ORGANIZATION

              British Virgin Islands
------------- -----------------------------------------------------------------
 NUMBER OF    7           SOLE VOTING POWER

   SHARES                 0
              ----------- -----------------------------------------------------
BENEFICIALLY  8           SHARED VOTING POWER

   OWNED                  2,874,000
              ----------- -----------------------------------------------------
  BY EACH     9           SOLE DISPOSITIVE POWER

 REPORTING                0
              ----------- -----------------------------------------------------
  PERSON      10          SHARED DISPOSITIVE POWER
                          2,874,000
   WITH
------------- ----------- -----------------------------------------------------
     11       AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

              2,874,000
------------- -----------------------------------------------------------------
     12       CHECK IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN
              SHARES |_|
------------- -----------------------------------------------------------------
     13       PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 11

              5.9%
------------- -----------------------------------------------------------------
     14       TYPE OF REPORTING PERSON

              CO
------------- -----------------------------------------------------------------



----------------------------                        ----------------------------
CUSIP No.  303250104            SCHEDULE 13D        Page 3 of 9 Pages
----------------------------                        ----------------------------

------------- -----------------------------------------------------------------
     1        NAME OF REPORTING PERSON

              Sandell Asset Management Corp.
------------- -----------------------------------------------------------------
     2        CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (a) |_|  (b) |_|
------------- -----------------------------------------------------------------
     3        SEC USE ONLY
------------- -----------------------------------------------------------------
     4        SOURCE OF FUNDS

              AF
------------- -----------------------------------------------------------------
     5        CHECK IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT
              TO ITEMS 2(d) or 2(e)     |_|
------------- -----------------------------------------------------------------
     6        CITIZENSHIP OR PLACE OF ORGANIZATION

              Cayman Islands
------------- -----------------------------------------------------------------
 NUMBER OF    7           SOLE VOTING POWER

   SHARES                 0
              ----------- -----------------------------------------------------
BENEFICIALLY  8           SHARED VOTING POWER

   OWNED                  2,874,000
              ----------- -----------------------------------------------------
  BY EACH     9           SOLE DISPOSITIVE POWER

 REPORTING                0
              ----------- -----------------------------------------------------
  PERSON      10          SHARED DISPOSITIVE POWER
                          2,874,000
   WITH
------------- ----------- -----------------------------------------------------
     11       AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

              2,874,000
------------- -----------------------------------------------------------------
     12       CHECK IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN
              SHARES |_|
------------- -----------------------------------------------------------------
     13       PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 11

              5.9%
------------- -----------------------------------------------------------------
     14       TYPE OF REPORTING PERSON

              CO
------------- -----------------------------------------------------------------



----------------------------                        ----------------------------
CUSIP No.  303250104            SCHEDULE 13D        Page 4 of 9 Pages
----------------------------                        ----------------------------

------------- -----------------------------------------------------------------
     1        NAME OF REPORTING PERSON

              Castlerigg International Limited
------------- -----------------------------------------------------------------
     2        CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (a) |_|  (b) |_|
------------- -----------------------------------------------------------------
     3        SEC USE ONLY
------------- -----------------------------------------------------------------
     4        SOURCE OF FUNDS

              AF
------------- -----------------------------------------------------------------
     5        CHECK IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT
              TO ITEMS 2(d) or 2(e)     |_|
------------- -----------------------------------------------------------------
     6        CITIZENSHIP OR PLACE OF ORGANIZATION

              British Virgin Islands
------------- -----------------------------------------------------------------
 NUMBER OF    7           SOLE VOTING POWER

   SHARES                 0
              ----------- -----------------------------------------------------
BENEFICIALLY  8           SHARED VOTING POWER

   OWNED                  2,874,000
              ----------- -----------------------------------------------------
  BY EACH     9           SOLE DISPOSITIVE POWER

 REPORTING                0
              ----------- -----------------------------------------------------
  PERSON      10          SHARED DISPOSITIVE POWER
                          2,874,000
   WITH
------------- ----------- -----------------------------------------------------
     11       AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

              2,874,000
------------- -----------------------------------------------------------------
     12       CHECK IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN
              SHARES |_|
------------- -----------------------------------------------------------------
     13       PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 11

              5.9%
------------- -----------------------------------------------------------------
     14       TYPE OF REPORTING PERSON

              CO
------------- -----------------------------------------------------------------



----------------------------                        ----------------------------
CUSIP No.  303250104            SCHEDULE 13D        Page 5 of 9 Pages
----------------------------                        ----------------------------

------------- -----------------------------------------------------------------
     1        NAME OF REPORTING PERSON

              Castlerigg International Holdings Limited
------------- -----------------------------------------------------------------
     2        CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (a) |_|  (b) |_|
------------- -----------------------------------------------------------------
     3        SEC USE ONLY
------------- -----------------------------------------------------------------
     4        SOURCE OF FUNDS

              AF
------------- -----------------------------------------------------------------
     5        CHECK IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT
              TO ITEMS 2(d) or 2(e)     |_|
------------- -----------------------------------------------------------------
     6        CITIZENSHIP OR PLACE OF ORGANIZATION

              British Virgin Islands
------------- -----------------------------------------------------------------
 NUMBER OF    7           SOLE VOTING POWER

   SHARES                 0
              ----------- -----------------------------------------------------
BENEFICIALLY  8           SHARED VOTING POWER

   OWNED                  2,874,000
              ----------- -----------------------------------------------------
  BY EACH     9           SOLE DISPOSITIVE POWER

 REPORTING                0
              ----------- -----------------------------------------------------
  PERSON      10          SHARED DISPOSITIVE POWER
                          2,874,000
   WITH
------------- ----------- -----------------------------------------------------
     11       AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

              2,874,000
------------- -----------------------------------------------------------------
     12       CHECK IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN
              SHARES |_|
------------- -----------------------------------------------------------------
     13       PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 11

              5.9%
------------- -----------------------------------------------------------------
     14       TYPE OF REPORTING PERSON

              CO
------------- -----------------------------------------------------------------



----------------------------                        ----------------------------
CUSIP No.  303250104            SCHEDULE 13D        Page 6 of 9 Pages
----------------------------                        ----------------------------

------------- -----------------------------------------------------------------
     1        NAME OF REPORTING PERSON

              Thomas E. Sandell
------------- -----------------------------------------------------------------
     2        CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (a) |_|  (b) |_|
------------- -----------------------------------------------------------------
     3        SEC USE ONLY
------------- -----------------------------------------------------------------
     4        SOURCE OF FUNDS

              AF
------------- -----------------------------------------------------------------
     5        CHECK IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT
              TO ITEMS 2(d) or 2(e)     |_|
------------- -----------------------------------------------------------------
     6        CITIZENSHIP OR PLACE OF ORGANIZATION

              Sweden
------------- -----------------------------------------------------------------
 NUMBER OF    7           SOLE VOTING POWER

   SHARES                 0
              ----------- -----------------------------------------------------
BENEFICIALLY  8           SHARED VOTING POWER

   OWNED                  2,874,000
              ----------- -----------------------------------------------------
  BY EACH     9           SOLE DISPOSITIVE POWER

 REPORTING                0
              ----------- -----------------------------------------------------
  PERSON      10          SHARED DISPOSITIVE POWER
                          2,874,000
   WITH
------------- ----------- -----------------------------------------------------
     11       AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

              2,874,000
------------- -----------------------------------------------------------------
     12       CHECK IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN
              SHARES |_|
------------- -----------------------------------------------------------------
     13       PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 11

              5.9%
------------- -----------------------------------------------------------------
     14       TYPE OF REPORTING PERSON

              IN
------------- -----------------------------------------------------------------



----------------------------                        ----------------------------
CUSIP No.  303250104            SCHEDULE 13D        Page 7 of 9 Pages
----------------------------                        ----------------------------

     The Schedule 13D filed on June 29, 2007, as amended by Amendment No. 1
filed on October 15, 2007, Amendment No. 2 filed on December 11, 2007, and
Amendment No. 3 filed on December 8, 2008 (the "Schedule 13D") by the Reporting
Persons (as defined below), relating to the common stock, par value $0.01 per
share (the "Common Stock"), of Fair Isaac Corporation, a Delaware corporation
(the "Issuer"), is hereby amended as set forth below by this Amendment No. 4 to
the Schedule 13D. Except as set forth herein, the Schedule 13D is unmodified.

ITEM 4.       PURPOSE OF TRANSACTION

Item 4 of the Schedule 13D is hereby amended and supplemented by the addition of
the following paragraphs prior to the penultimate paragraph of such Item 4:

     As of July 24, 2009, Mr. Graziano ceased to be employed by SAMC and as a
result is no longer affiliated with the Reporting Persons. While Mr. Graziano
will remain as a member of the Issuer's board of directors, he will no longer
serve in such capacity as a representative of SAMC or the other Reporting
Persons. The Issuer and the Reporting Persons have amended the Amended and
Restated December 7 Agreement to remove from such Agreement the Reporting
Persons' right, under certain circumstances, to replace three directors named to
the Issuer's board pursuant to such Agreement, and to make certain related
changes.

     The foregoing description of the Amendment No. 1 to the Amended and
Restated December 7 Agreement is a summary only and is qualified in its entirety
by reference to such Amendment No. 1, a copy of which is filed herewith as
Exhibit F and is incorporated by reference into this Item 4.

ITEM 5.       INTEREST IN SECURITIES OF THE ISSUER

Paragraphs (a) and (c) of Item 5 of the Schedule 13D are hereby amended and
restated as follows:

(a) Each of Castlerigg Master Investments, SAMC, Castlerigg International,
Castlerigg Holdings and Sandell may be deemed to beneficially own the 2,874,000
shares of Common Stock held by Castlerigg Master Investments, representing
approximately 5.9% of the outstanding shares of Common Stock. The Reporting
Persons may be deemed to be a "group," which "group" may be deemed to
beneficially own an aggregate of 2,874,000 shares of Common Stock, representing
approximately 5.9% of the outstanding shares of Common Stock. The percentages
used herein are based upon the 48,852,923 shares of Common Stock reported to be
outstanding as of April 30, 2009 by the Issuer in its report on Form 10-Q for
the quarterly period ended March 31, 2009, filed with the Securities and
Exchange Commission on May 7, 2009.

(c) No transactions in the shares of Common Stock were effected by the Reporting
Persons during the past sixty days.



----------------------------                        ----------------------------
CUSIP No.  303250104            SCHEDULE 13D        Page 8 of 9 Pages
----------------------------                        ----------------------------

ITEM 6.       CONTRACTS, ARRANGEMENTS, UNDERSTANDINGS OR RELATIONSHIPS WITH
              RESPECT TO SECURITIES OF THE ISSUER

Item 6 of the Schedule 13D is hereby amended and supplemented by the addition of
the following paragraph:

     As described in Item 4 above, the Issuer and the Reporting Persons have
entered into an Amendment No. 1 to the Amended and Restated December 7 Agreement
to remove from such Agreement the Reporting Persons' right, under certain
circumstances, to replace three directors named to the Issuer's board pursuant
to such Agreement, and to make certain related changes. The foregoing
description of Amendment No. 1 to the Amended and Restated December 7 Agreement
is a summary only and is qualified in its entirety by reference to such
Amendment No. 1, a copy of which is filed herewith as Exhibit F and is
incorporated by reference into this Item 6.

ITEM 7.       MATERIAL TO BE FILED AS EXHIBITS

     The following documents are filed as appendices and exhibits:

Appendix III:   Information Regarding the Instruction C Persons

Exhibit A:    Letter to Issuer's Chief Executive Officer dated June 29, 2007
(previously filed)

Exhibit B:    Press release issued by Sandell Asset Management Corp. on
June 29, 2007 (previously filed)

Exhibit C:    Agreement by and among the Reporting Persons and the Issuer, dated
as of December 7, 2007 (previously filed)

Exhibit D:    Press Release dated December 10, 2007 (previously filed).

Exhibit E:    Amended and Restated Agreement by and among the Reporting Persons
and the Issuer, dated as of December 4, 2008 (previously filed).

Exhibit F:    Amendment No. 1 to the Amended and Restated Agreement, by and
among the Reporting Persons and the Issuer, dated as of July 29, 2009.



----------------------------                        ----------------------------
CUSIP No.  303250104            SCHEDULE 13D        Page 9 of 9 Pages
----------------------------                        ----------------------------

                                    Signature

     After reasonable inquiry and to the best of my knowledge and belief, I
certify that the information set forth in this statement is true, complete and
correct.

     Dated: July 29, 2009

            CASTLERIGG MASTER INVESTMENTS LTD.
            By:  Sandell Asset Management Corp.,
                 as investment manager

            By: /s/ Thomas E. Sandell
                ---------------------
                Thomas E. Sandell, Chief Executive Officer


            SANDELL ASSET MANAGEMENT CORP.

            By: /s/ Thomas E. Sandell
                ---------------------
                Thomas E. Sandell, Chief Executive Officer


            CASTLERIGG INTERNATIONAL LIMITED
            By:  Sandell Asset Management Corp.,
                 as investment manager

            By: /s/ Thomas E. Sandell
                ---------------------
                Thomas E. Sandell, Chief Executive Officer


            CASTLERIGG INTERNATIONAL HOLDINGS LIMITED
            By:  Sandell Asset Management Corp.,
                 as investment manager

            By: /s/ Thomas E. Sandell
                ---------------------
                Thomas E. Sandell, Chief Executive Officer


            /s/ Thomas E. Sandell
            ---------------------
            Thomas E. Sandell