Mr. Brooks (Kevin Costner) realizes that his daughter Jane killed the college student, and that is the reason she dropped out of college. He goes and kills someone else the same way she did so that she won't be a suspect any longer. He is upset that she has the same addiction he does, and worries, because of his alter-ego Marshall (William Hurt) that she may kill him someday.
He wants to stop killing, so he decides to have Mr. Smith (Dane Cook) kill him after he takes him on his first kill. Mr. Brooks, with Mr. Smith, kills Det. Atwood's (Demi Moore) ex-husband and his lawyer and gives her information on how to find the escaped killer she's also been looking for. He helped her because he respects the fact that she made herself into a good cop even though she came from money and didn't need to.
When Mr. Brooks takes Mr. Smith to a cemetery to have him kill him, he changes his mind, killing Mr. Smith instead and tossing him into an open grave. He calls Atwood anonymously, indirectly letting her know that Smith wasn't the Fingerprint Killer. That night at home, as he kisses his daughter good-night, she turns and stabs him in the neck with a pair of scissors. As he dies, he wakes up...the last part was a nightmare. Mr. Brooks tries to go back to sleep reciting the Alcoholics Anonymous prayer.