Part 1
Part 2

Part 3
Part 4

The Big Nurse tries to undermine McMurphy by posting a statement showing that since he arrived, all the Acutes have been steadily losing money, while he has been steadily gaining it. This is because of McMurphy’s success as a gambler. The Acutes do not seem to mind this much, since McMurphy is very open about it. But they do start to wonder why McMurphy is doing so many things on their behalf. They wonder what is in it for him. At a group meeting which McMurphy does not attend, the Big Nurse discusses him with the group. She insinuates that he only appears to be helping the men. In reality he is only out for himself. After the meeting, one by one the men begin to agree with the Big Nurse. The only exception is Bromden, who still has faith in McMurphy. McMurphy gets him to lift the control panel in the tub room, which McMurphy himself had earlier failed to lift. This shows Bromden that McMurphy has kept his promise to make him big again. Knowing that the control panel can be moved, McMurphy takes some bets on it. The men still believe that it cannot be moved. But of course Bromden is able to do so. McMurphy gives him a share of the winnings, but Bromden refuses it. He feels that he helped McMurphy to cheat.

In the shower room that afternoon, the men who went on the fishing trip are ordered to take a special shower to ensure they are not carrying parasites. George refuses to accept an enema, and protests loudly. McMurphy intervenes on his behalf, and gets into a fight with Washington, one of the black boys. Warren, one of the other black boys, pins McMurphy’s arms from behind, but Bromden pulls him off and throws him into the shower. Another black boy grabs Bromden from behind, and Bromden runs backward and smashes him against the shower tiles.

Aides from the Disturbed ward arrive and McMurphy and Bromden are handcuffed. They are taken to Disturbed, where they spend the night. The following morning, they refuse the medicine they are given prior to receiving electric shock treatment. The Big Nurse arrives and tells McMurphy can be let off EST if he admits that he was in the wrong. McMurphy refuses.

He and Bromden watch as two men go into the room where the EST is given. After those men are wheeled back out on a gurney, McMurphy tries to give Bromden courage, and says he will go first. He shows no fear. He is bound down and given the electric shock, which makes his whole body jerk violently. Then it is Bromden’s turn. He is lost in memories of his childhood. But afterwards he makes a quick recovery, rather than getting lost for up to two weeks in the “fog” that usually follows such treatments.

McMurphy receives three more shock treatments that week. He has no fear of them and they appear to have little effect on him, although Bromden notices the strain on his face whenever he is called for another treatment. The men realize that the treatments will continue indefinitely for McMurphy, since the Big Nurse wants to defeat him. She wants the other patients to stop making a hero of him and to see how vulnerable he is. The men therefore decide that the best course of action is for McMurphy to escape. But their escape plan coincides with the day McMurphy had planned to bring Candy onto the ward for Billy. McMurphy says there is no hurry to escape.

At the next group meeting, the Big Nurse suggests that an operation should be considered for McMurphy. McMurphy turns the discussion into a joke at the expense of the Big Nurse.

That night Candy and her friend Sandy are smuggled into the ward. McMurphy has bribed the night duty aide, Mr. Turkle, so the girls are not detected. They bring bottles of port wine and vodka with them. Everyone gathers in the day room. A supervisor turns up and they all hide in the latrine while Mr. Turkle assures the supervisor that everything is fine. Then they pick the lock on the drug room and get some drugs to mix with the alcohol. They look at their own medical files in the Nurses’ Station, and then sit around the day room, drinking, smoking and laughing. They grab some wheelchairs from storage and race up and down the hall. After four o’clock, Candy and Billy go together into the Seclusion Room.

As morning approaches, Harding is the only man who is deeply concerned about the repercussions of their party. Since McMurphy is too drunk to organize anything, Harding takes over. His plan is that they tie Mr. Turkle up so that it will look as if McMurphy had set upon him, gathered up the drugs and scattered the medical files, and then escaped. McMurphy should make his escape with the girls and drive with them to Canada or Mexico. McMurphy agrees to leave at about six. Before that he plans to get some sleep, and Turkle agrees to wake McMurphy and Candy up in an hour. But the plan goes wrong. Turkle fails to wake them, and they are discovered by the black boys at six-thirty that morning.

In the confusion that follows, McMurphy has a chance to escape, since the screen that bars the window is unlocked. But McMurphy is still half-drunk and declines the opportunity. Harding is still the only man who realizes the gravity of the situation.

A count of the patients reveals that Billy Bibbit is missing. A search is begun, and Billy is found with Candy in the Seclusion Room. The Big Nurse is furious. She indicates that she plans to tell Billy’s mother about the incident. Billy begs her not to, but the Big Nurse insists that she has to. Billy blames McMurphy and the others for forcing him to do it. The Big Nurse takes him away to the doctor’s office.

The doctor arrives, but when he goes to see Billy, he finds that Billy has killed himself by cutting his throat. The Big Nurse blames McMurphy and rebukes him. She walks into the Nurses’ Station, but McMurphy follows and attacks her. He rips her clothes, exposing her breasts, and then tries to strangle her. He is eventually pulled off her by hospital officials.

Over the next two weeks, there are changes in the ward. Sefelt and Frederickson sign out from the ward, and three other Acutes leaves. Six more are transferred to another ward. When the Big Nurse returns, she has visible signs of her injuries, and can communicate only by writing notes. She informs the men, in answer to Harding’s question, that McMurphy will be back.

The Big Nurse’s power has gone. Harding checks out of the ward, and George is transferred to a different ward. That leaves only Bromden, Martini and Scanlon of the original Acutes.

One day, McMurphy is wheeled in on a gurney. He has had a lobotomy (removal of part of the brain) and his expression is blank. Scanlon and Martini refuse to believe it is really him. Knowing that McMurphy would not want to live in such a vegetable-like state, Bromden suffocates him with a pillow. Scanlon tells him that the Big Nurse will know that he killed McMurphy, and advises him to flee. Scanlon says he will concoct a story that he saw McMurphy move about after Bromden left, which will mean that Bromden will not be considered guilty. Bromden goes to the tub room and lifts the heavy control panel, since McMurphy had already shown him that he could do it. He carries the control panel and smashes the screen and window with it. Then he jumps through the window and runs in the direction of the highway. He catches a ride with a Mexican man going north. He plans to return to the village in which he grew up.

Analysis
The parallels that emerged in Part 3 between Christ and McMurphy are continued. Encouraged by the Big Nurse, the men lose faith in McMurphy (as some of the disciples betrayed Christ) and decide that he is only out for himself. Then, after the fight in the shower room, the men—no doubt encouraged by the Big Nurse—agree that McMurphy should have EST. Just before this takes place, in the Disturbed ward an old man sees McMurphy and says, “I wash my hands of the whole deal,” (p. 264) which recalls Pontius Pilate’s similar statement that he washes his hands of Jesus’ fate. The process of EST is described in ways that resemble the crucifixion of Christ. “Do I get a crown of thorns?” McMurphy asks.

The men do regain their confidence in McMurphy, and the wild and uninhibited (and often very amusing) night-time party shows how McMurphy is liberating them. As Bromden points out (p. 292), by having the party in the midst of a citadel of the Combine’s power, they have shown that the Combine is not all-powerful. It can be defied and beaten.

Like Christ, McMurphy dies a sacrificial death. Others are saved by it. He breaks the power of the Big Nurse, enabling most of the men to voluntarily leave the ward. He also enables Bromden to escape, since had it not been for McMurphy, Bromden would never have believed that he was strong enough to lift the control panel.