McMurphy shows up in the ward one morning and moves around among the men, both Acutes and Chronics, introducing himself and avoiding the shower required upon admission to the ward.
He finds out who’s top dog—Harding—and says he intends to be the big man on the ward from now on. Their showdown is over Eisenhower—whoever voted for him the most is the craziest guy there. McMurphy wins.
Nurse Ratched approaches him to say he’s being difficult about his shower but he must follow the rules. He responds that in his experience, the only time somebody reminds him about the rules is if they think he doesn’t intend to follow them.
In his first afternoon group meeting, McMurphy observes how Nurse Ratched pits all the men against one another. After the meeting is over, he describes it as a "pecking party" and suggests that Nurse Ratched is leading all the men to peck each other’s balls off. She’s emasculating them.
McMurphy makes a bet with the guys that he can break Nurse Ratched without destroying himself.
After his morning shower, McMurphy shows up in only a towel. He claims his clothes were stolen. Nurse Ratched finds out his old clothes were taken away and his green asylum uniform hasn’t yet arrived but she’s furious to see him half-naked in the hall.
McMurphy tries to get Nurse Ratched to turn the music in the day room off, but she politely tells him that this wouldn’t be fair to the Chronics, who can’t relieve their boredom through card games the way the Acutes can. So McMurphy suggests that the Acutes could meet in the tub room to play cards, but she says there’s not enough staff for it.
During the next afternoon meeting, the doctor says he’s had a long talk with McMurphy and he thinks that a carnival would be good for the guys. Nurse Ratched clearly doesn’t like the idea and says it must be discussed in a staff meeting first.
McMurphy then brings up the tub room again, with the doctor’s support, who says they have plenty of staff for the tub room plan. So McMurphy has scored a point against Nurse Ratched.
McMurphy’s next idea is switching the cleaning schedule so the men can watch the World Series in the afternoon. When he can’t get enough guys to back him up, he tells them later that they’re gutless.
He brings the vote up again at the next meeting. Nurse Ratched agrees to put the matter to a vote, even though she’s furious. All the Acutes raise their hands—twenty of them. But she says that that’s not a majority since the Chronics didn’t raise their hands, so the schedule will not be changed.
McMurphy goes around to the Chronics, begging one of them to raise their hand. But, the Chronics don’t get it—until Chief raises his hand.
The next afternoon, McMurphy goes and turns the television to the baseball game. Nurse Ratched turns the television off from the nurses’ station. McMurphy watches the blank television in protest, as if the game were really on. The Acutes join him and they watch the blank TV screen.
The afternoon meetings become a gripe session and McMurphy doesn’t even need to lead off.
McMurphy finds out that Nurse Ratched has the power to keep him there in the asylum as long as he wants, and that changes his perspective. At the next meeting, when Cheswick brings up the issue of cigarettes, McMurphy is silent. He doesn’t back Cheswick up, even though Cheswick is sent to Disturbed Ward.
McMurphy sees how Frederickson and Sefelt need their medication to prevent seizures but it rots their gums out. They’re damned if they do take medicine and damned if they don’t. This has special resonance for him in terms of his rebellion against Nurse Ratched.
McMurphy discovers that most of the men are in the ward voluntarily—he’s one of two Acutes who have actually been committed. When he discovers this, he’s astounded and asks why the men stick around. That’s when he realizes that most of the men are too afraid to be out in the "real world."
At the next meeting, Nurse Ratched plays her hand, thinking McMurphy is sufficiently cowed this time. She says the men are to be punished for their little rebellion.
McMurphy stands up, walks over to where she’s sitting, and busts his hand through the Nurses’ Station window.
Nurse Ratched leaves him alone for a long time after that, and he begins to plan a fishing fieldtrip for all the men.
When McMurphy discovers that Chief can hear and speak after all, he signs Chief up for the fishing trip. Because Chief thinks he’s a small man now, McMurphy offers to help him "get big" again.
The fishing trip is successful and McMurphy manages to get laid.
McMurphy and Chief get into a fight with the orderlies in order to protect Rub-a-Dub George. They’re sent to the Disturbed Ward where they undergo electroshock therapy.
McMurphy becomes a small legend because he refuses to admit he was wrong, even though it means perpetual punishment with electroshock therapy.
Two weeks later, when he’s back on the ward, McMurphy manages to sneak Candy and Sandy on the ward. They have a major ward party, where they all get drunk and Billy and McMurphy go to bed with the two prostitutes.
When they’re discovered, Nurse Ratched shames Billy so badly that he commits suicide. McMurphy is so angry that he smashes a glass door and assaults Nurse Ratched.
When McMurphy returns from the hospital, he’s no longer McMurphy—he’s had a lobotomy.
Chief smothers McMurphy to death in his hospital bed.