Randle Patrick McMurphy is an Irish American brawler found guilty of battery, gambling and statutory rape. He is a Korean War veteran who was a POW during the war and was awarded the Distinguished Service Cross for leading a breakout from a Chinese camp, but was dishonorably discharged for insubordination. He is sentenced to a fairly short prison term and decides to have himself declared insane in order to be transferred to a mental institution, where he expects to serve the rest of his time in comparative comfort and luxury.
McMurphy's ward in the mental institution is run by the tyrannical Nurse Ratched, who has cowed the patients into submission. McMurphy makes it his mission to flout Ratched's regime of rules and punishment and to liberate the other patients from her grip.
During his short stay at the hospital, McMurphy forms deep friendships with two of his fellow patients: Billy Bibbit, a manchild who has a stutter, whom Ratched has dominated into a suicidal mess; and Chief Bromden, a selectively mute Native American. In the former, McMurphy sees a younger brother figure whom he wants to teach to have fun, while the latter is his only real confidant.
McMurphy becomes ensnared in a number of power-games with Nurse Ratched. He ends up as the clear winner, reminding the other patients how to enjoy life and stand up for themselves, and persuading them to act out against Ratched's bullying. Ratched unsuccessfully tries to break his spirit through repeated shock therapy treatments.
In the novel's climax, McMurphy sneaks two prostitutes into the ward to take Billy's virginity, while he and the others throw a party. Ratched catches them and threatens to tell Billy's mother—the only woman he fears more than her—which terrifies him so much that he commits suicide by slitting his throat. Enraged, McMurphy assaults her and chokes her nearly to death, but is knocked unconscious by one of the hospital's orderlies. For this, Ratched has McMurphy lobotomized, which is to be seen as a kind of castration: "If she [Ratched] can’t cut below the belt she’ll do it above the eyes".[2] Chief Bromden, seeing what Ratched has done to McMurphy, smothers him with a pillow in an act of euthanasia, and then breaks a window to flee from the asylum, fulfilling McMurphy's wish for him to be free. Nurse Ratched, meanwhile, has been rendered unable to speak after McMurphy's assault, breaking her hold over her patients.
