Lights, camera, action!
Let's get up close and personal with our main character, shall we?
The opening credits to Fight Club take place inside the human body, perhaps filmed by the Magic School Bus. It emerges from our narrator character (we know what his nerve endings look like but not his name; that's too personal) played by Edward Norton, who has a gun in his mouth, held there by Tyler Durden (Brad Pitt).
How'd our narrator get into this predicament? We're about to find out. David Fincher is too classy for a wavy flashback effect, but what follows is about two hours of flashback.
Our narrator, suffering from chronic insomnia, is attending support groups. Not for insomnia, but for diseases he doesn't have: brain parasites, tuberculosis, and testicular cancer. At his testicular cancer support group, he meets a man with giant breasts named Bob and learns how to cry. That night, he sleeps.
Then Marla Singer (Helena Bonham Carter) shows up. She's a faker, a tourist, going to support groups for diseases she doesn't have. She's exactly like our narrator, and he can't take it. They divide up the support groups so they never have to see each other again.
On a business trip, our narrator meets Tyler Durden, a charming soap salesman. When our narrator returns home, he has no home to return to. His apartment has exploded: either arson or some really flammable IKEA furniture. He calls Tyler Durden and grabs a drink with him. Tyler agrees to let our narrator stay at his house, but first he wants a favor: "I want you to hit me as hard as you can." The two fight in the parking lot of Lou's Tavern, and then go home to Tyler's dilapidated house on Paper Street.
Every night they go the tavern and fight, and other men join them. Eventually, fight club is born. We'd recap the rules, but even if you've never seen this movie, you know them. Also, we're not allowed to talk about them, like, at all.
One day the phone rings at the Paper Street house. It's Marla. (How'd she get this number?) She's taken a bunch of sleeping pills and is dying. Our narrator doesn't care…but Tyler picks up the phone and decides to go to her apartment. He brings her home and she tells him, "You're gonna have to keep me up all night." Tyler does, but at least they take safety precautions. There are a few "precautions" floating in the toilet when our narrator goes to use it in the morning. Marla comes over often, and our narrator tries his best to ignore her and Tyler's house-shaking sex sessions.
When Marla finally beats it, Tyler takes our narrator to procure some fat for soap. Where do you get fat? The dumpsters behind the liposuction clinic, of course. They steal some gooey bags and Tyler renders it down to soap, while talking about how it can also be used to make explosives.
He also kisses our narrator's hand and sprinkles lye on it, causing a severe chemical burn. Yowza. It's all to help him hit rock bottom, and when Tyler assesses that our narrator has reached a new low (or high, when it comes to pain) he douses the burn with vinegar.
As fight club grows, Tyler starts assigning homework. The first assignment: get into a fight with a stranger, and lose. Our narrator chooses his boss, and frames his boss into beating him up, which earns him a hefty settlement check from his employer.
Eventually, fight club morphs into Project Mayhem, and the homework assignments become more destructive: blowing up coffee shops and computer stores, threatening the police, and working toward some top secret master plan which our narrator is kept in the dark about.
One night, Tyler purposefully gets the narrator into a car accident (another of those "rock bottom" things) and disappears. Our narrator tries to find him, and boy does he. He discovers that he is Tyler Durden. He and Tyler are the same person! He realizes that he knows Tyler's plan: to blow up a bunch of credit card companies, so he tries to stop it. However, Project Mayhem has spread to a point that all the building's security guards are in Project Mayhem, so if our narrator wants to stop the explosions, he'll have to do it himself.
He defuses one bomb and gets into a fight with Tyler, er, himself, which leads us back to where we were at the very beginning: Tyler/Narrator holding a gun to his own head. Whew, what a trip.
In order to "kill" Tyler, our narrator shoots himself in the head…he somehow lives, but Tyler—who never existed in the first place—dies. Marla shows up, dragged to the building by Project Mayhem goons, and our narrator tells her, "Everything's gonna be fine. […] You met me at a very strange time in my life." He takes her hand as the other buildings explode and fall around them. Cue credits. The end.