Patrick Bateman is a wealthy investment banker living in Manhattan in the late 1980s. His life revolves around dining at trendy restaurants while keeping up appearances for his fiancée, Evelyn, and for his circle of wealthy and shallow associates, most of whom he dislikes. Bateman describes the material accoutrements of his lifestyle: his daily morning exercise and beautification routine, his music collection including performers such as Huey Lewis and the News, Phil Collins, and Whitney Houston, his taste for expensive designer clothes, and the lavish couture of his apartment.
Bateman and his associates flaunt their business cards in a display of vanity. Enraged by the superiority of coworker Paul Allen's card, Bateman murders a homeless man and his dog. At a Christmas party, Bateman makes plans to have dinner with Paul. Bateman gets Paul drunk and lures him back to his apartment. While playing "Hip to Be Square" on the stereo, Bateman ambushes Paul and murders him with an axe. He disposes of Paul's body, then goes to Paul's apartment to stage the situation so that others believe Paul has run off to London. Bateman is met by Donald Kimball, a detective investigating the disappearance.
Bateman takes two prostitutes, whom he names Christie and Sabrina, to his apartment and lectures them about the improvement he saw in the band Genesis after Phil Collins replaced Peter Gabriel. After they have sex, Bateman tells them to stay. They leave his apartment bruised and bloodied.
The next day, Bateman's colleague Luis Carruthers reveals his new business card. Bateman tries to kill Luis in the restroom of an expensive restaurant, but cannot bring himself to strangle him. Luis mistakes the attempted murder for a sexual advance and declares his love for Bateman, who flees in disgust. After murdering a model, Bateman invites his secretary, Jean, to dinner, suggesting she meet him at his apartment for drinks beforehand. When Jean arrives, Bateman, unbeknownst to Jean, holds a nailgun to the back of her head while the two converse. When he receives an answering machine message from his fiancée, he asks Jean to leave. Kimball meets Bateman for lunch and tells him he is not under suspicion.
Bateman has a threesome with Christie and his friend Elizabeth at Paul's apartment. Bateman kills Elizabeth during sex, and Christie runs, discovering multiple female corpses as she searches for an exit. Bateman drops a chainsaw down a flight of stairs, killing her.
Bateman breaks off his engagement with Evelyn. That night, as he uses an ATM, he finds a stray kitten; the ATM displays the text "feed me a stray cat". As he prepares to shoot the cat, a woman sees him and tries to stop him; he shoots her. A police chase ensues, but Bateman destroys the police cars by shooting their gas tanks. Fleeing to his office, Bateman enters the wrong office building, where he murders a security guard and a janitor. In his office, Bateman calls his lawyer Harold and leaves a lengthy confession on Harold's answering machine.
The following morning, Bateman visits Paul's apartment, expecting it to be full of decomposing bodies, but it is vacant and for sale. The real estate broker tells him to leave. As Bateman goes to meet with his colleagues and lawyer, Jean finds detailed drawings of murder and rape in Bateman's office journal.
Bateman sees Harold at a restaurant and tries to convince him that he is a serial killer. Harold mistakes him for another colleague and laughs off the confession as a joke, saying he had dinner with Paul in London days earlier. Bateman realizes he will continue to escape the punishment he deserves, that there has been no catharsis, and that his confession has meant nothing.