Plot

The narrator (Edward Norton) is a nameless automobile company employee who travels to accident sites for the purposes of calculating whether or not to issue product recalls based on the likely cost of lawsuits that would be incurred otherwise. His doctor refuses to write a prescription for his insomnia, and instead recommends that he visits a support group for testicular cancer sufferers to appreciate real suffering. The narrator attends the group and is able to find catharsis, sleeping soundly without a problem.

During a flight for a business trip, the narrator meets Tyler Durden (Brad Pitt), a flamboyant soap salesman. When the narrator arrives home, he finds that his apartment has been destroyed by an explosion. He calls Tyler and meets him at a bar, where Tyler permits the narrator to stay at his place. Leaving the bar, Tyler asks the narrator to hit him. The narrator reluctantly complies, and the two end up enjoying a fist fight. The narrator moves in with Tyler at an abandoned house, and they continue fighting outside the bar, attracting a crowd and eventually establishing a 'fight club' in the basement. Eventually more clubs spring up around the country.

Meanwhile, the narrator's routine is again disrupted when he notices another person faking these illnesses (like himself), Marla Singer (Helena Bonham Carter), whose presence at his support groups again disrupts his ability to sleep. Marla overdoses on Xanax and is rescued by Tyler Durden. The two begin a sexual relationship, and Tyler forbids the narrator from talking to Marla about him.

Eventually, Tyler's fight club becomes "Project Mayhem," which commits acts of anti-corporate vandalism in the city. The fight clubs become a network for Project Mayhem, and the narrator is left out of Tyler's activities with the project, feeling disillusioned and disturbed about their actions. Tyler and the narrator have an argument and Tyler disappears from the narrator's life.

When a member of Project Mayhem, Bob (Meat Loaf), dies on a mission, the narrator decides to take action to shut down the project. He tries to trace Tyler's steps, traveling all over the country and feeling a sense of déjà vu wherever he travels. Puzzled, he calls Marla Singer, and asks her to say his name. When she responds "Tyler Durden," he realizes the truth; Tyler is an alter ego of his own split personality. Tyler appears in his room and explains that he is in control of the narrator's body whenever he is asleep. The narrator falls unconscious, and he wakes to find phone calls made during his blackout. He tracks Tyler's plans to the downtown headquarters of major credit card companies, which Tyler plans to destroy to collapse the consumerist financial system. The narrator, attempting to disarm the explosives in the building basement, is confronted by Tyler, knocked unconscious, and taken to the upper floor of another building to witness the impending destruction.

The narrator, held by Tyler at gunpoint, realizes that, sharing the same body with Tyler, he really holds the gun. He finds himself holding the gun and fires it into his mouth, shooting through the cheek without killing himself. The illusion of Tyler collapses, with an exit wound to the back of his head. Members of Project Mayhem, who still see the narrator as Tyler, bring Marla Singer to him and leave them alone, despite being shocked by his wound. Marla, who was warned to leave the city by the narrator, concernedly asks what happened. The narrator explains that he shot himself and tells her, "You met me at a very strange time in my life." They watch as the buildings explode in a collapsing skyline outside the windows, standing side-by-side and holding hands.