Tyler and the narrator are standing on top of the one hundred and the ninety story Parker-Morris building on the edge of total destruction. Tyler is holding a gun in the narrator's mouth and pressing the barrel against the back of this throat.

This is the end of a story that starts two years before. The narrator is an average run-of-the-mill worker, who lives his life on repeat. He has a great condo and participates avidly in the consumer culture of society. He is suffering from severe insomnia and can't figure out why. The narrator finds a remedy for his insomnia by going to support groups and crying with the real injured people. It is there he meets Marla Singer, who completely throws his regular support-group meeting schedule out of alignment. He despises her for intruding in his territory.

During the course of a normal work business trip, the narrator happens to meet a man named Tyler Durden while hanging out on the beach. The narrator gets Tyler's phone number. When the narrator arrives home from the business trip, he finds that his condo exploded and all his possessions are destroyed. With nowhere to turn, he calls upon Tyler Durden for help. Tyler meets with him, and they end up fighting in the parking lot. This is the beginning of fight club.

The narrator moves in with Tyler in his Paper Street house. Time goes by, and more and more people join fight club. Fight club expands to incorporate new locations and more members. The desire to fight and the feeling that it brings to the participants is spreading across the male population.

Back at the Paper Street house, Tyler and a woman named Marla met and are now having sex. This leaves the narrator feeling jealous, and all he can think about is them humping non-stop. It is even invading his dreams.

Tyler starts rendering fat to make soap, and it turns into a lucrative business. Eventually, Tyler and the narrator decide to blackmail their bosses. It turns out they know too many secrets and have nothing to lose. The narrator starts to notice that he is becoming more like Tyler as the days go by. His face is beat up like Tyler's, and Tyler's words start flowing out of his mouth.

Tyler decides to turn his small acts of civil disobedience into an entire project. He calls it Project Mayhem. Project Mayhem contains several small committees that meet for various assignments during the week. The narrator soon finds himself sucked into the project and on assignment like the rest of the Project Mayhem members.

The narrator is going about his business and traveling like normal when he realizes that he is being treated with an unusual level of respect by guys with bashed-in faces. After some investigation, the narrator discovers that it is his face that people recognize as that of Tyler Durden. The narrator is Tyler Durden. While the narrator sleeps, his split personality Tyler takes over his body and carries out his destructive manifesto. The narrator feels Tyler becoming more dominant, and he is getting out of control.

Shortly after the narrator realizes that he is Tyler, one of the Project Mayhem space monkeys, Bob, gets killed. At this point, the narrator knows that things have gone too far. He attempts to put a stop to Project Mayhem and cancel fight club. He is unsuccessful, and the whole thing is out of his control. He knows the only way to stop all of it is to get rid of Tyler.

The narrator arrives at work to find that the building is blown up, and his boss is dead. He remembers that the last time he left the office he smelled gasoline on his hands. As he tries to flee to avoid getting questioned by the police, he gets on a bus full of space monkeys who insist they have orders from him, but really Tyler, to castrate him for trying to stop fight club and Project Mayhem. The narrator passes out from this traumatizing event and wakes up on the floor of his burned condo.

He realizes that if the space monkeys have orders to harm him, Tyler may have given orders to harm Marla too. He meets Marla. She slaps him and tells him that he killed someone. The narrator is not shocked by this as he knows that he killed his boss. That is not it, however. Marla followed Tyler, and he went to a murder-mystery dinner where he proceeded to kill the mayor's special envoy on recycling. As Marla has witnessed first hand the crimes that Tyler is committing, the narrator fears that Tyler will neutralize anyone who dares get in the way of Project Mayhem.

The memories of the murder of the mayor's special envoy come flooding back to the narrator's brain. He wants to be dead. The narrator finds a fight club meeting and signs up to fight all the men in the room. He is beaten to a pulp, and surprised that his body has such an amazing will to live despite the fact that he wants to be dead. He wakes up in his room in the Paper Street house, and Tyler is there. The whole place is empty. Tyler drags him onto the roof of the Parker-Morris Building. They are back in the place where the story begins. The clock is ticking down, and the narrator is waiting for the building to explode.

The time comes and goes with no explosion. Apparently, Tyler mixed the chemicals wrong. The narrator feels he has no choice but to shoot himself. He has to make Tyler disappear. The narrator survives the shooting and gets put into a mental institution. In the institution, he is cared for by members of fight club. They assure him that everything is going as planned and that they are looking forward to his return.