A montage sequence begins as Jack flies from city to city retracing Tyler’s steps. Jack says that he has the feeling he’s been to these places before. He finds evidence of other fight clubs in existence. He is recognized on the street by men with bruises on their faces. It seems that Tyler is building a nationwide army. Jack enters a bar where the bartender recognizes him and welcomes him back. Jack has no recollection of this man. The bartender wears a neck brace and his face is puffy and bruised. Jack asks the man how he knows him. The bartender answers that he was there last week asking about security. “Who do you think I am?”, asks Jack. The bartender answers, “You’re Mr. Durden. You’re the man who gave me this.” The bartender holds up his hand to show Jack his lye scar.
Jack bursts into his hotel room and calls Marla. He asks her about the nature of their relationship. She calls him Tyler. Jack begins to break out into a cold sweat. Marla says she’s coming over and hangs up. Jack hangs up and suddenly Tyler is seated in the hotel room with him. Jack asks him what is going on. “Why do people think I’m you?”, he asks, frightened. Jack soon realizes that he and Tyler are actually the same person. Tyler is a persona Jack takes on, a mental projection he sometimes imagines other people interacting with. Tyler says that Marla thinks they are the same person but might figure things out. He feels she knows too much and she has to be dealt with. Jack faints.
Jack wakes up again to find Tyler gone. He checks out of the hotel to find out he has been billed for phone calls made between 2 and 3 am, calls that Tyler must have made while he was “asleep”. Jack now understands that he hasn’t been sleeping at all. He’s just been Tyler at night.
Jack returns to an empty house. He begins calling the phone numbers on the hotel bill. They all match large buildings and office structures. When he dials the number he is connected with an employee at each building. They all appear to be manned by Project Mayhem members.
Jack scrambles out of a taxi on Marla’s block. He sees her exiting her building and calls after her. She doesn’t want to see him. He follows her and gets her to agree to hearing him out. They sit down at a restaurant table. The waiter tells Jack that whatever he orders there is free. The entire staff appear to also be Project Mayhem members. Jack insists on clean food for he and Marla. He explains to Marla that he does care about her and that she needs to get out of town for a while. She finds this to be absurd and gets up to leave. Jack follows her outside. He steps in front of a city bus which screeches to a halt. He gives Marla whatever money is in his pockets and tells her to get on the bus and go without telling him where she’s headed. She reluctantly does so. As the bus doors close she says, “Tyler, you’re the worst thing that ever happened to me.”
Jack goes to the police station and asks them to arrest him. He meets with Detective Stern and spills the details about Project Mayhem. The plan, Jack believes, is to blow up the headquarters of several major credit card companies, erasing the debt record. Detective Stern exits the interrogation room, leaving Jack with several police officers. They reveal themselves to also be members of Project Mayhem. One of them steps forward. “We really admire you, sir. You said if anyone tries to interfere with Project Mayhem, even you, we gotta get his balls.” They swarm around Jack, one of them producing a knife. They pin him down but he manages to grab one of their guns and escapes.
Jack arrives at Franklin St., where one of the target buildings is located. He descends to the garage level of the building where he finds a van full of explosives. Tyler appears and begins ridiculing him as Jack tries to disarm the bomb. Jack is successful. Tyler attacks him and they begin fighting. Tyler throws Jack down some stairs. Jack loses consciousness.
Jack regains consciousness with Tyler holding a gun in his mouth. We are now at the initial moment of the film. Tyler has found a spot for them to watch the explosions: an unfinished floor of an office building looking out over the city skyline. Jack begs Tyler to call off the detonation. Tyler tells Jack to take some responsibility for creating him. Jack can see that he is losing his own personality, soon he will only be Tyler. A commotion outside alerts Jack to the fact that space monkeys have found Marla. They carry her inside to meet up with Jack and Tyler. “Tying up loose ends,” says Tyler. Jack sees the gun in Tyler’s hand. He thinks and realizes that Tyler isn’t holding the gun, he is. He puts the gun in his own mouth. Tyler tries to play this off as inconsequential but for the first time we can see that he is concerned. If Jack is dead, so is he. Jack pulls the trigger and blows a hole through his own cheek. Tyler blows a smoke ring out of his mouth and drops to the ground, “dead.” The space monkeys come in with Marla. Jack instructs them to leave her and go and find some gauze for his face. They leave the two of them as the detonation commences. Tall office buildings in the background begin to crumble. Jack and Marla hold hands. He looks at her. “You met me at a very strange time in my life.”
In this final segment of the film the truth about Tyler and Jack's relationship is finally revealed. There are numerous clues throughout the film but Jack finally learns from Marla that he and Tyler are actually the same person. The awkward triangle that Jack believed existed between them wasn't actually a triangle at all. Jack is now faced with a frightening new reality: he could lose his entire persona and life to Tyler. Tyler could become the dominant personality, eliminating Jack entirely.
Jack now sees that if he lets himself become Tyler there will no longer be a Jack. He is actually the only person who can stop Tyler. Marla is the only other person who could discern the true nature of Tyler and Jack's relationship and therefore is a threat to Tyler and his plans. Tyler uses no euphemisms to explain his position. Marla has to be eliminated. Tyler has finally reached a point beyond which Jack cannot progress. He is forced to confront his feelings on Marla. He has to stop Tyler to save her and himself.
He scrambles to find her and try to explain that he is sorry. He confesses that he cares about her deeply though she is convinced he is insane. Given the circumstances, this is understandable. Jack's descent into this madness has already tested her patience greatly. Jack's request to her to leave town feels equally like an attempt to get rid of her and the insane ramblings of a mad man. Jack tells Marla that he is aware that he must seem like he has two sides to his personality. Marla says that Jack is "Dr. Jekyll and Mr. Jackass," referencing the classic fictional split-personality case in the novel by Robert Louis Stevenson. Tyler is a monstrous creation that Jack brings into being only to find that he cannot control Tyler. Tyler, in turn, becomes more powerful and comes to dominate his creator's life. The narrative stays with Jack, the positive personality, as he tries to undo Tyler's work.
Jack's disadvantage in trying to stop Tyler is that they share a mind. Tyler is aware that Jack might go to the police, which he does. The officers there inform him that he might try to talk his way out of his situation. When Jack finds Tyler in the garage at Franklin St. he turns the tables by using their shared mind to his advantage. Tyler becomes enraged when Jack diffuses the bomb. Jack's persona is asserting itself and it is getting in Tyler's way. Jack continues to use their shared mind to his advantage even after Tyler throws him down the staircase. He is able to gain control of the situation when he realizes that he's the one holding the gun, not Tyler. When he puts it to his own head, Tyler is forced into a corner. He tries to bargain his way out. "Hey. You and me," he says, trying to reassert their friendship. Tyler has no intention of there being a Jack and a Tyler. During the duration of the film, Jack's appearance deteriorates while Tyler's becomes more and more idealized, a symbolic representation of Tyler as the dominant personality in Jack's mind, to show that he is getting stronger while Jack is becoming weaker. To rid himself of Tyler, Jack has to go farther than Tyler ever would. He shoots himself through the cheek to symbolically kill Tyler. When the Space Monkeys arrive upstairs to find the seriously injured Jack they are impressed with his strength, proving that Jack had this capacity inside him all along. He doesn't need Tyler. What he does need is an antidote to the loneliness that isolated him in the first place: Marla. He takes her hand as the buildings detonate outside, indicating that they are now able to embark on a real relationship together.
Jack's defeat of Tyler allows him to reach a middle ground between the ideals of his old life and the ones Tyler espoused. Tyler has freed him from his past attachments but Marla has allowed Jack to actually accept himself. Hers is the healthier of Jack's relationships though he wasn't aware of it throughout the entire film. His newly found freedom is a rebirth that can allow him to be happy. Though Marla clearly has some issues of her own, her redeeming quality is that she doesn't hide from them. She embraces them. This, more than anything, is what disturbs Jack about her. By demonstrating her vulnerability she shows a strength that Jack doesn't. Instead he invents Tyler to become a sort of Nietzschean Ubermensch because this is how he feels he needs to be to deal with his life and the world. The persona of Tyler gives him the license and strength to change his life. Marla is seemingly attracted to Tyler for his physical and sexual prowess, but she still thinks he and Jack are the same person. She believes him to be the man she met at the support group meetings. She breaks their pact to seek him out because she wants to connect with him. Jack desires the same thing but it isn't until Tyler threatens to remove Marla from the equation that Jack understands it. Removing Marla would allow Tyler to exact total control over Jack and eliminate his personality permanently.
The film examines the world of men in contemporary society in a way few films today do. The themes are not only applicable to men, however. We increasingly reside in a sterile world in which we are more likely to participate only as spectators. The rise of reality television and the internet have only made that more possible. We engage less and less in activities ourselves anymore. Without that regular exposure to visceral experiences, we live lives with less excitement, seeking it out in a consumer lifestyle or an emulated experience like a video game. Ultimately, each of us is responsible for our own lives. Jack doesn't garner much sympathy from the doctor or Tyler early on in the film because he complains about his life constantly but does nothing to change it. Tyler's maxim that we all need to know and not fear that one day we will die is not meant to be depressing. It is simply a fact. If we keep that in mind, each of us may affect positive change in our own lives.