We back out of the webbing of neurons and brain cells as the title credits appear, finding ourselves emerging from the sweat-glistened skin of the protagonist: our narrator (Edward Norton
), as he looks down the barrel of a gun that's been stuck in his mouth. The gun is held by a man named Tyler (Brad Pitt
) who checks his watch, counting down to 'ground zero' before he asks if the narrator has anything to say. The narrator mumbles through the gun before it's removed and reiterates that he can't think of anything. As Tyler looks out of the high rise window to the dark city below them, the narrator recalls just how he met Tyler before stopping himself and bringing us to the very beginning.
In six months, the narrator hasn't slept. His job as a traveling product recall specialist for a car company doesn't help his insomnia since he must travel often, experiencing bouts of jet lag in addition to the everyday stress of his position, admiring the 'tiny life' of single-serving soap and shampoo at every location. If he can't sleep, he surfs the channels or browses through Ikea catalogs purchasing the next piece of decor to add to his apartment; he's a self-proclaimed slave of consumerism. He goes to his doctor seeking help, but all the doctor can do is suggest that he visit a support group for testicular cancer to see real pain. There, the narrator meets Robert 'Bob' Paulson (Meat Loaf
), the 'big moosie' and an ex-bodybuilder and steroid user who suffers from an extreme case of gynecomastia due to hormone treatment after his testicles were removed. Stuck between Bob's enormous chest, the narrator finally finds peace and bursts into tears. The emotional release allows him to sleep and he subsequently becomes addicted to support groups, mapping out his week attending different meetings and feigning illness. However, the appearance of a woman named Marla Singer (Helena Bonham Carter
) throws the narrator's 'system' out of whack. He recognizes her as a 'tourist', having seen her at multiple meetings, and he is disturbed by her lies to the point where he can't sleep anymore.
After one meeting, he confronts her. She argues that she's doing exactly what he does and quips that the groups are 'cheaper than a movie and there's free coffee'. Instead of ratting each other out, they agree to split up the week and exchange numbers. Despite his efforts, the narrator's insomnia continues. On a flight back from one of his business trips, the narrator meets Tyler Durden. Tyler offers a unique perspective on emergency procedure manuals in the plane and they strike up a casual conversation. Tyler is a soap salesman, if he's not working nights as a projectionist and slipping bits of porn between reels. The narrator arrives at the baggage claim to discover that his suitcase has been confiscated, most likely due to a mysterious vibration, before he taxis home. However, home, a fifteenth story condominium, has been blasted into the night by what was theorized to be a faulty gas line ignited by a spark on the refrigerator. Having nowhere to go, the narrator finds a business card for Tyler and calls him up. They meet in a parking lot behind a bar where Tyler invites the narrator to ask to come live with him...on one condition: that the narrator hit Tyler as hard as he can. The narrator, though puzzled, complies and they engage in a fist fight before sharing a couple of drinks. The experience is surprisingly euphoric.
Tyler and the narrator engage in more fights over the coming days and they soon attract the attention of other 'tough guys'. Finding their little fighting group growing, Tyler establishes a formal 'fight club' in the basement of the bar where they had their first fight. Membership quickly increases and Tyler and the narrator fashion a series of rules, the first two being 'you do not talk about fight club.' The rules are consistently broken. Time and again, Tyler proves his insightful, if unorthodox and immoral, views on life.
The narrator meets up with Marla by chance, telling her that he hasn't attended any other meetings because he's joined a new support group for men only.
While he still treats her with mild contempt, it's clear that he considers her with interest. When she overdoses on Xanax, she calls the narrator who, tired of her rambling, sets the phone down. He discovers later that Tyler picked up the phone, followed the call to Marla's home, and brought her back to the house where they engaged in vigorous sex, much to the narrator's disgust. The next morning in the kitchen, Marla finds the narrator, who is astonished to see her in his house. After she leaves, Tyler enters the kitchen and reveals that he and Marla had sex the night before. He also gravely makes the narrator promise that he'll never mention Tyler to Marla.
That night the narrator joins Tyler while he steals human fat out of the dumpster of a liposuction clinic. Tyler says that the best fat for making the soap he sells comes from human beings. Back in their kitchen, Tyler shows the narrator how to render tallow from the fat. After explaining a bit about the history of soapmaking, Tyler plants a wet kiss on the back of the narrator's hand and dumps pure lye on the spot, causing a horrific chemical burn. Tyler refuses to let the narrator wash the lye off his hand, saying that water will worsen the burn, and tells the narrator that the burn is a rite of passage -- Tyler has burned his own hand in an identical way. Tyler also forces the narrator to accept allegiance to him and then neutralizes the burn with vinegar. Later, when they meet with a cosmetics salesperson at a department store, the narrator remarks that Tyler's soap sells for a very high price.
With the narrator, he holds a college dropout (Joon Kim
) at gunpoint and threatens to kill him if he doesn't pursue his dream of becoming a veterinarian. He allows Lou (Peter Iacangelo
), the owner of the bar where their fight club is held, to beat him up before coughing blood all over him and demanding to stay in the basement. Horrified, Lou agrees.
After a period of days, Marla leaves and Tyler introduces the narrator to his newest hobby. Using his proficient skills in soap-making, Tyler has turned the basement of the house into a laboratory where he uses soap and other ingredients to make explosives. Tyler and the narrator continue managing fight club, but this time, at a much different frequency. Receiving flack at work, the narrator finally confronts his boss (Zach Grenier
) with knowledge about substandard practice and negotiates to work from home with increased pay to keep his mouth shut. When his boss objects and calls security, the narrator begins to beat himself up severely so that, by the time security arrives, they are led to believe that the narrator's boss did that to him.
Tyler eventually assigns homework to his recruits and preaches to them about the detriments of consumerism and relying on society and authority figures. He proposes to revert back to the time where a man's worth depended on the sweat on his back and where he only used what he needed. This philosophy evolves into what Tyler calls 'Project Mayhem,' and the fighting in basements turns into mischievous acts of vandalism and destruction. Their actions do not go unnoticed, but Tyler manages to show the lead investigator that the very people he's hunting are those that they depend on; waiters, bus drivers, sewer engineers, and more. The dilapidated house where Tyler and the narrator live turns into Mayhem central, where each new recruit is put through a rigorous period of initiation and training and where the latest plans are hatched. While Project Mayhem grows, the narrator begins to feel more and more distant from Tyler and jealousy sets in, making him go so far as to beat up and disfigure one recruit (Jared Leto
) because he 'wanted to destroy something beautiful'. When Tyler disappears for a while, the narrator is left at home with an ever increasing band of Mayhem members who watch television and laugh at their publicized acts of vandalism. When Bob, a member after being introduced to Fight Club, is killed during a botched sabotage operation, the narrator seeks to disband the group before things get out of control. He tries to find Tyler and discovers a list of phone numbers he recently used. The narrator trails the list all over the country, discovering that fight clubs have sprouted everywhere.
At one particular bar, the bartender addresses the narrator as 'sir' which prompts the narrator to ask if he knows him. The bartender, after being assured that he's not being put through a test, tells the narrator that he is Tyler Durden. In shock, the narrator returns to his hotel room and calls up Marla, asking if they'd ever had sex. Though irritated, Marla confirms their relationship and states that she knows his name as Tyler Durden. Marla hangs up and Tyler suddenly appears in the room and confronts the narrator, confirming that they are, indeed, one person. The narrator has insomnia; he can't sleep so, whenever he thinks he is (or at random parts of a day), Tyler's persona takes over. The epiphany causes the narrator to faint. When he wakes up, he finds another phone list beside him with calls from all over the country.
He returns to his home to find it completely empty but one billboard yields a display of folders detailing certain buildings within the financial district. He finds that each one has been infiltrated by members of Project Mayhem and that Tyler is planning on destroying them, thereby erasing credit card company records and 'wiping the slate clean'. In a panic, the narrator grabs all the information and reports himself to the local police. However, after telling the inspector everything he knows and being left with two officers, the narrator discovers that the officers are Mayhem members and they tell him that they were instructed by him to 'take the balls' of anyone who interfered with Project Mayhem...even him. The narrator manages to escape and runs to one of the buildings set for demolition. He finds an unmarked van in the parking garage filled with nitroglycerin and attempts to disarm the bomb. Tyler appears and goads him but the narrator successfully disarms the bomb. He and Tyler engage in a fierce fight which appears oddly on the surveillance cameras since the narrator is only fighting himself. The Tyler personality wins and the narrator 'brings himself' to another building where they can safely watch the destruction.
This brings us back to where we started. The narrator, with the gun in his mouth, mumbles again and tells Tyler, "I still can't think of anything". Tyler smiles and says, "Ah, flashback humor". The narrator begs that Tyler abandon the project but Tyler is adamant. He professes that what he's doing is saving mankind from the oppression of consumerism and unnecessary luxuries and that there won't even have to be any casualties; the people who work in the buildings are all Mayhem members, completely aware of the plan. Near breaking point, the narrator comes to realize that whatever Tyler does, he can do. He sees Tyler with the gun in his hand and realizes that it's actually in his hand. He puts it up to his own chin and tells Tyler to listen to him. He says that his eyes are open and then puts the gun in his mouth and pulls the trigger. The bullet shoots out of the side of his jaw and Tyler is 'killed' with a gaping wound to the back of his head. As the narrator recovers, members of Project Mayhem arrive with snacks and Marla in tow (Tyler had previously instructed her to be brought to them).
Seeing 'Tyler's' wounds, the Mayhem members leave Marla alone with him to fetch some medical supplies. 'Tyler' stands with Marla and tells her that everything's going to be fine as the first detonation ignites the building in front of them. The others on the block soon follow suit and 'Tyler' takes Marla's hand in his as the buildings collapse and the film reel ends.