The novel begins with an unnamed Narrator sitting on the top floor of a skyscraper that’s about to explode, with a man named Tyler Durden pointing a gun into his mouth. The novel is told almost entirely in flashbacks.
Some time before, the Narrator develops insomnia. Bored with his corporate, consumerist lifestyle, he starts attending cancer support groups, despite the fact that he doesn’t have cancer. The support groups allow the Narrator to express strong emotions and sleep well. But soon, another “faker” begins attending the groups: a woman named Marla Singer. Marla explains that she goes to the support groups because she wants to feel “close to death.”
The Narrator takes a vacation and, on a beach, he meets a strange man named Tyler Durden, who gives the Narrator his phone number. When the Narrator returns home, he finds that his condominium has exploded. With nowhere else to go, he calls Tyler, who allows the Narrator to crash at his house for a while. One day, Tyler convinces the Narrator to hit him as hard as he can; reluctantly, the Narrator does so. Tyler and the Narrator then realize that they love fighting, because it makes them feel alive and “real.”
While the Narrator sleeps at Tyler’s house, he continues working at his corporate job, which requires him to travel around the country calculating the cost of recalling dangerous cars his company has built. Tyler, meanwhile, works odd jobs as a waiter at a hotel and a projectionist in a movie theater. Tyler uses his jobs to sabotage society: he urinates in fancy dishes at the hotel, and splices single frames of pornography into family movies. Tyler and the Narrator found a secret society called “fight club,” in which members fight one another in order to get in touch with visceral reality and their own masculinity.
Tyler receives a call at his house from Marla, and goes to Marla’s hotel. Following this incident, Tyler and Marla begin having loud, frequent sex in the house, irritating the Narrator. Tyler tells the Narrator not to mention him in front of Marla, or the Narrator will never see Tyler again. Tyler also shows the Narrator his other source of income: making soap and selling it to fancy department stores. During one soap-making session, Tyler kisses the Narrator’s hand and pours lye it, giving him a scar that looks like “Tyler’s kiss.” Tyler insists that he’s trying to get the Narrator to embrace death and pain so that he can find enlightenment.
Marla regularly stops by Tyler’s house to drop off shipments of collagen, removed from her mother’s aging body by liposuction. Secretly Tyler converts the collagen into beautiful, creamy bars of soap, which he sells for a big profit—when Marla finds out, she’s furious. The Narrator notices that he, Tyler, and Marla are never in the same room together.
Marla calls the Narrator and asks him to examine her for breast cancer; they learn that she does have breast cancer, and afterwards, Marla begins attending cancer support groups for real. Meanwhile, the police call the Narrator and tell him that they suspect that someone—possibly the Narrator himself—blew up his condominium. Meanwhile, fight club becomes bigger and bigger, to the point where other chapters spring up across the country.
Tyler forms a new secret society within the secret society, called Project Mayhem. Tyler subjects his Project Mayhem recruits to a brutal initiation process, and afterwards urges them to sacrifice their own happiness and identity for the good of the movement. Tyler hosts hundreds of Project Mayhem members in his house, all of whom are slavishly loyal to him. He also sends out his followers on missions to “destroy society,” often through bombings or vandalism. The Narrator continues to keep Marla company and support her through her struggle with cancer.
One evening, The Narrator gets a call at work from Tyler, telling him to get into a Project Mayhem car waiting for him. The Narrator does so, and the driver, a mechanic, swerves the car on and off the road while asking The Narrator, “What did you want to do before you died?” The Narrator answers, “Quit my job.” As they drive, the Narrator becomes so depressed with the meaningless of his own life that he tries to drive the car into oncoming traffic—the Mechanic prevents him from doing so.
While Project Mayhem goes on as usual, Tyler disappears altogether. The Narrator, confused, tries to track down Tyler by going to different bars and clubs. Each time, the bartenders address him as “Sir.” Eventually, the Narrator realizes the truth: everyone thinks that he is Tyler Durden. The Narrator calls Marla and she, too, addresses him as Tyler. Suddenly, Tyler appears before the Narrator and explains that he’s the Narrator’s alter ego. He and the Narrator share the same body, but Tyler is braver and more charismatic than the Narrator—he’s The Narrator’s unconscious, the wish fulfillment of his repressed desires. The Narrator has been the one having sex with Marla, organizing Project Mayhem missions, and converting human fat into soap and explosives. The Narrator, frightened of what he’s becoming, tells Marla the truth.
The Narrator tries to shut down Project Mayhem and the fight club, only to realize that “Tyler” has prepared his loyal followers for such a possibility: the members throw the Narrator out and begin keeping tabs on him. The Narrator discovers that his boss has died in a freak explosion, and he realizes that Tyler and Project Mayhem are responsible. Project Mayhem tracks down the Narrator, addressing him as “Mr. Durden,” and prepares to castrate him for his disloyalty. The Narrator loses consciousness.
The Narrator wakes up in the ruins of his old condominium, (he hasn’t been castrated). He considers committing suicide, but realizes that he cares about Marla and has to protect her. He finds Marla, who tells him that “he” (as Tyler) has murdered more people. The Narrator loses consciousness again, and finds himself at the top floor of a skyscraper (right where he was at the beginning of the novel). Tyler explains that “they” will now die in a blaze of glory.
Suddenly, Marla and the members of her cancer support group walk into the skyscraper, where they find the Narrator pointing a gun at himself. The timer for the bomb goes off, but nothing happens—the Narrator realizes that Tyler and Project Mayhem must have used faulty explosives. Nevertheless, he shoots himself in the face.
In the final chapter of the book, the Narrator reveals that his suicide attempt didn’t work: he shot through his neck and ear, leaving him injured but alive. Tyler hasn’t disturbed him since his suicide attempt. Marla writes him letters while he recovers in the hospital. Occasionally, members of Project Mayhem stop by and, addressing him as “Mr. Durden,” say that they’re eager for him to get back to work.