For a three-act plot analysis, put on your screenwriter’s hat. Moviemakers know the formula well: at the end of Act One, the main character is drawn in completely to a conflict. During Act Two, she is farthest away from her goals. At the end of Act Three, the story is resolved.
Act I
Stephen Rojack is an ex-congressman and television host. Although he's been married to Deborah Kelly—a wealthy heiress—for eight years, their relationship has started to deteriorate. This leaves Rojack seriously depressed, even contemplating suicide. Instead of killing himself, though, Rojack rushes over to Deborah's apartment to see her, but ends up strangling her to death in a fit of rage. Uh oh.
Act II
Rojack kicks into action, throwing Deborah's body out the window to make it seem like a suicide. He also sleeps with her maid. Deborah's fall causes a car accident, so the police are already waiting; a detective named Roberts introduces himself.
Rojack meets Cherry, a smoking hot nightclub singer. Although Rojack is brought to the police station, he manages to beat the suspicions of the police. Then, of course, he hooks up with Cherry. Their brief moment of bliss is interrupted, though, by the entrance of Shago Martin, Cherry's ex. Rojack manages to beat the boogers out of Shago, but he can't hang around to celebrate his victory—after all, he has an appointment to meet Barney Kelly, Deborah's father.
Act III
Our not-so-humble antihero arrives at Kelly's apartment. The vibe is weird immediately, but it gets so much weirder when Kelly reveals that he and Deborah had a brief affair. Gross.
Kelly convinces Rojack to walk along the guardrail on the porch, thinking that Rojack will fall to his death. Somehow, however, he manages to make it all the way around, celebrating his victory by smacking Kelly in the face and running away. There's nothing good waiting for him, though: Cherry has been murdered. At this point, Rojack goes even crazier, leaving NYC for Las Vegas, and then Guatemala. We're sure he'll be up to no good upon his arrival.