The unnamed Narrator is an automobile recall specialist who is unfulfilled by his job and possessions. He finds catharsis by posing as a sufferer of testicular cancer and other afflictions in support groups, curing his insomnia. His bliss is disturbed by another impostor, Marla Singer. The two agree to split which groups they attend.
On a flight home from a business trip, the Narrator meets soap salesman Tyler Durden. The Narrator returns home to find that his apartment and all his belongings have been destroyed by an explosion. He is disheartened by the loss of his material possessions. Deciding against asking Marla for help, he calls Tyler, and they meet at a bar. Tyler says the Narrator is beholden to consumerism. In the parking lot, he asks the Narrator to hit him, and they begin a fistfight.
The Narrator moves into Tyler’s home, a large dilapidated house in an industrial area. They have further fights outside the bar, which attract growing crowds of men. The fights move to the bar’s basement where the men form Fight Club, which routinely meets for the men to fight recreationally.
Marla overdoses on pills and telephones the Narrator for help; he ignores her, but Tyler goes to her apartment to save her. Tyler and Marla begin a sexual relationship, much to the Narrator’s irritation. Tyler warns the Narrator never to talk to Marla about him. The Narrator blackmails his boss for his company’s assets to support Fight Club and quits his job.
Soon, Fight Clubs begin to form across the country. New members begin to join en masse, including Robert Paulson, a man with testicular cancer who the Narrator had previously met in a support group. Tyler recruits their members to a new anti-materialist and anti-corporate organization, Project Mayhem, without the Narrator’s involvement. The group engages in subversive acts of vandalism and violence, increasingly troubling the Narrator. After the Narrator complains that Tyler has excluded him, Tyler leaves the house. The Narrator realizes that Tyler caused the explosion at his apartment.
When Paulson is killed by the police during a botched sabotage operation, the Narrator tries to halt the project. He follows a paper trail to cities Tyler has visited. In one city, a Project Mayhem member addresses the Narrator as “Mr. Durden.” Confused, the Narrator calls Marla and discovers that she also believes he is Tyler. Tyler appears in his hotel room and reveals that they are dissociated personalities in the same body; the Narrator assumed the personality of Tyler when he believed he was sleeping.
The Narrator blacks out. When he returns to the house, he uncovers Tyler’s plans to erase debt by destroying buildings that contain credit card records. He apologizes to Marla and warns her that she is in danger, but she is tired of his contradictory behavior and refuses to listen. He tries to warn the police, but the officers are members of the Project. He attempts to disarm the explosives in one building, but Tyler subdues him. With Tyler holding him by gunpoint in the top floor, the Narrator realizes that, as he and Tyler are the same person, he is holding the gun. He fires it into his own mouth, shooting through his cheek, which causes Tyler to collapse since he thinks he has committed suicide; the Narrator ceases mental projection of Tyler. Project Mayhem members bring a kidnapped Marla to the building. Holding hands, the Narrator and Marla watch as the explosives detonate, collapsing buildings around them.