Patrick and his opulent coworkers Justin Theroux, Josh Lucas, and Bill Sage usually gather in Hotel Dastelle to discuss more ways to flaunt their wealth. They then go to a pub, where Patrick orders a Stoli vodka, and the bartender insists on cash rather than a credit card. He becomes enraged and responds with rage that he wants to stab her to death and play with her blood. Patrick Bateman is a 27-year-old wealthy New York City investment banker who is more beauty conscious and follows a strict exercise regimen and a balanced diet every morning.
He consults with his secretary, Miss. Jean confirms three reservations: one in Camols and two in Arcadia. Out of the blue, he remarks that she looks good in skirts and suggests wearing the same with heels. Evelyn Williams is Bateman’s fiancee and keeps buzzing around him. Bateman is the one who spends most of his time in 1987 dining at popular restaurants while maintaining appearances for his fiancée Evelyn Williams and his circle of wealthy associates, the majority of whom he despises. He is also having an affair with her best friend, Courtney Rawlinson, an engaged blonde with nearly perfect looks.
The next day, he gets into an argument with the washerwoman, demanding that he remove the stains on the bed sheets. She refuses, stating that it is impossible to remove. Another known woman, Victoria, enters the laundry, and Bateman asks her assistance in resolving the same problem with the washerwoman. He asks her to sort it out, and then he walks away from the door. He asks Courtney to go on a date with him to Dorsia the next day. Then he attempts to book a reservation in Dorsia but is unsuccessful. On the date night, Courtney is inebriated and concocts the lie that BARCADIA is Dorsia.
Another businessman named Allen Paul communicates with Mr. Bateman, who is considered Marcus. Sadly, when he departs, he adds that he had reserved a table at Dorisa for a Friday night, which had left his pals with a better impression of him. At a business meeting, Bateman and his colleagues show off their business cards, emphasizing their design and style. Bateman, enraged by the superiority of his colleague Paul Allen's card, kills a homeless man and his dog in an alley for no reason at night.
After a Christmas party, Bateman and Allen, who misidentifies Bateman as Marcus, another coworker, make dinner plans. Allen's affluent lifestyle and ability to secure reservations at Dorsia, an exclusive restaurant, irritate Bateman. While listening to Huey Lewis and the News, he gets Allen drunk, lures him to his apartment, and murders him with an axe. Bateman disposes of the body before entering Allen's apartment and leaving a message on his answering machine claiming that Allen has gone to London.
Donald Kimball, a private investigator who has been hired by Meredith Powell to investigate the case regarding Allen Paul’s disappearance, now interviews Bateman. He quickly tries to hide the dark CDs, magazines, and headphones under his desk. Donald also mentions that Allen was possibly seen in London. Bateman invites two prostitutes with money, Christie and Sabrina, to his apartment for sex. He records a sexual videotape with them. He tortures them, pays them, and dispatches them.
When Bateman is having a routine gathering with his colleagues, Luis Carruthers interrupts and reveals a new business card. He gets jealous and attempts to strangle him in an expensive restaurant's restroom. Carruthers misinterprets the attempts and initiates to have homosexuality with him and declares his love for Bateman, who panics and flees. For further inquiry, Kimball pays Bateman another visit and inquires as to where he was on the night of Paul's disappearance. Bateman plays it off as being uncertain, and Kimball ends by inviting him for lunch the next week.
He has sex with Courtney, who advises him to have a nice one if he can't meet her before Easter. He meets a model in a pub the next night and tempts her to go with him after taking drugs with his colleague. He then murders her and freezes her severed head. The next day, he invites his secretary, Jean, to dinner and invites her to meet him for drinks at his apartment. When she does, Bateman is about to murder her with a nail gun. Coincidentally, he receives a message on his answering machine from Evelyn, and then he stops his action of murdering her and asks her to move out of his place.
After having lunch with Kimball, Bateman learns that a coworker of his claims to have eaten dinner with him the night of Allen's disappearance, which strengthens his alibi. Kimball observes that the idea of one of Allen's friends murdering him for no apparent reason is simply unfathomable, to which Bateman nervously responds. Bateman contacts Christie, the same prostitute, once again that evening. She tries to decline, but he persists in inviting her by seducing her with cash. After bringing Christie to Allen's apartment, Bateman gives his friend Elizabeth some drugs before having sex with both of them. Christie flees after Bateman kills Elizabeth and finds several female corpses as she looks for a way out. While she runs down a stairwell, a naked Bateman pursues her, attacks her with a running chainsaw, and murders her. Soon after, the next evening, he meets Evelyn and cancels his engagement with her.
While using an ATM, Bateman notices a cat. He prepares to shoot the cat after seeing the text "FEED ME A STRAY CAT" on the ATM. When a woman confronts him, he shoots her instead. Even though there is a subsequent police pursuit, Bateman kills several policemen by shooting one officer and detonating a patrol car. Before hiding in his office, Bateman murders a security guard and a janitor. He frantically leaves a confession on his lawyer Harold Carnes's answering machine, confessing to having killed 20–40 people and eaten some of their brains. Bateman returns to Allen's apartment the next morning to clean it, but it is vacant and for sale. A realtor asks him to leave and not return after cryptically stating that the apartment does not belong to Allen.
Bateman calls Jean while in a hysterical state before heading to lunch with his colleague. Bateman's work journal contains graphic, in-depth drawings of murder and mutilation, which Jean discovers in the meantime. Bateman approaches Carnes and discusses the phone message they had last night. Bateman is misidentified by Carnes as a different man, and the confession is dismissed as a joke. Bateman clarifies his identity and confesses to the murders once more, but Carnes dismisses his claims as impossible because he recently dined with Allen in London. Bateman returns to his friends bewildered; they talk about dinner plans and speculate on whether Ronald Reagan is a kindly old man or a covert psychopath. Bateman realizes he will never receive the punishment for his desires because he is unsure whether his crimes were real or imagined. His narration declares that he is constantly in pain, that he wishes his pain on others, and that his confession is meaningless.
