At an Oregon mental asylum, serene but tyrannical Nurse Ratched maintains firm control over the men’s ward. In the day room, calm music blares from a record player, as she and her assistant, Nurse Pilbow, hand out daily medications to their patients. Randle Patrick McMurphy, who is eager to escape a work farm prison where he is serving a six-month sentence for statutory rape, is delivered to the asylum wearing handcuffs. When McMurphy attempts to greet a very tall Native American, called Chief Bromden, he is met with a blank stare and no response. Billy Bibbit, the youngest patient in the ward who has a marked stutter, informs McMurphy that Bromden is a deaf-mute. When the hospital psychiatrist, Dr. Spivey, meets with McMurphy, he tells him that the prison officials believe McMurphy is faking mental illness and informs him that the hospital staff will be evaluating him to determine whether he should be returned to complete his sentence or remain at the asylum. McMurphy arrives at Ratched’s ward as she is leading a group therapy session in which she urges the men to discuss the marital and sexual problems of Harding, a well-spoken, educated patient who suspects his wife of infidelity. The men are at first reluctant to speak up, but Ratched encourages them to talk. Due to the intrusive nature of the discussion, Harding becomes upset, causing tension to rise within the group. The session ends with loud arguments that prompt the orderlies to physically remove some of the patients out of the room to restore the peace. During an outdoor exercise interval, McMurphy encourages Bromden to play basketball by climbing onto the shoulder of another patient and shooting the ball through the hoop, but Bromden shows little interest. Later, McMurphy encourages his fellow patients to play blackjack, instead of their usual pinochle, using cigarettes to represent dimes. When McMurphy asks Ratched to turn down the music so the men can hear each other, Ratched refuses, explaining that the older men who are hard of hearing would not be able to enjoy it. McMurphy balks at taking medication, but Ratched convinces him to cooperate by offering to administer the medicine in another way. At the next group session, McMurphy suggests changing the work detail, so that the men can watch the opening of the World Series on television. Ratched patiently explains that making changes would disturb the men in the ward who take a long time adjusting to a schedule. She suggests taking a vote, but most of the men are reluctant, even fearful, of voting against her will. Later, in the “tub room” of the asylum, McMurphy suggests that they leave the asylum to watch the game at a bar, but the men explain that they are locked in. McMurphy bets them that he can get them out and attempts to lift a large marble washing station with which he plans to break open a window, but finds it too heavy. When he finally gives up, he tells the others that at least he tried. At the next group session, Ratched focuses on Billy, who had asked a girl to marry him. Ratched mentions that Billy’s mother never told Ratched about the girl, which causes Billy’s stutter to intensify. When she asks about the first time he tried to commit suicide, another patient, Cheswick, asks Ratched why she presses Billy on the subject when he does not wish to talk. Changing the subject, he says that he would like to see the baseball game and asks for another vote. This time, all nine men in the group vote in favor of the game, but Ratched tells them that there are eighteen patients in the ward and a majority vote is needed to change ward policy. McMurphy approaches each of the other men, urging them to raise their hands, but they are too mentally ill to comprehend the events around them. Just as Ratched ends the group meeting, McMurphy convinces Bromden to raise his hand, but Ratched again refuses to give in, claiming that the vote was closed. Refusing to be defeated, McMurphy stares at the blank television screen and pretends to watch the game, shouting out a play-by-play commentary that inspires the other men to join him and cheer. After his fourth week at the asylum, McMurphy meets with Spivey, as other doctors observe their conversation. When he is asked if he likes being at the asylum, McMurphy responds that Ratched is not honest, that she “likes a rigged game.” Spivey tells McMurphy that he diagnoses no evidence of mental illness, prompting McMurphy to make silly faces and other odd movements, and ask, “Is this crazy enough for you?” As the men are preparing to go on an outing, McMurphy impulsively asks Bromden to help him over the barbed wire fence around the hospital. On the other side, he hides in the vacant bus until the men board, then drives the bus away, leaving the asylum staff behind. After picking up Candy and Rose, friendly prostitutes with whom he is acquainted, he takes the men to a marina, where he convinces the harbor master to let them charter a boat, introducing himself and his cohorts as doctors from the mental institution. He teaches the men to bait a hook and puts Cheswick in charge of the ship’s wheel, while Billy and Candy go below deck. When the men later return to the waiting police who accompany Spivey, they are exhilarated. Later, the panel of doctors meet and cannot agree on whether McMurphy is mentally ill, but some believe he is dangerous. When they consider returning him to the prison, Ratched suggests that they keep him rather than relinquish their problems to another institution. Outside, McMurphy leads the men in a game of basketball. Bromden walks back and forth between the two baskets, ensuring that his own team’s ball goes into the basket while preventing the opposing team’s ball from going through, but everyone enjoys the game. During a hydrotherapy session, McMurphy mentions to one of the orderlies that he has only sixty-eight days left of his sentence, but is told that, unlike a prison sentence, asylum commitments last until the doctors allow you to leave. At the next group session, McMurphy accuses his fellow patients of not explaining that he must remain there at the discretion of Ratched and the doctors. Harding says that he did not know, as he had voluntarily committed himself, and Ratched explains that McMurphy is one of only a few who are actually committed. Hearing that Billy could leave if he wished, McMurphy tells him that he is young and should be out enjoying women. He tells the men they are no crazier than most people. When Ratched encourages comments on McMurphy’s statement, the men direct their challenges at her, by asking why the doors to their rooms are locked during the day and why their cigarettes are withheld from them. When the usually docile Cheswick demands his cigarettes, Ratched accuses McMurphy of creating the necessity of rationing their cigarettes, because he was winning their money and cigarettes in gambling. A patient, Taber, who has been hiding a lit cigarette in the cuff of his pants, yells out in pain when it burns his leg, creating chaos that builds when Cheswick loudly demands his cigarettes and disturbs the more vulnerable patients. To calm him, McMurphy breaks the window of the nurses’ office to retrieve his cigarettes. Meanwhile, Washington, an orderly, tries to force Cheswick from the room, prompting McMurphy to punch him. They fight, but when Washington holds McMurphy down, the silent Bromden comes to his aid. Order is restored when more orderlies are called in, and McMurphy, Bromden and Cheswick are cuffed and taken from the room to be given sedatives. While waiting in a hall, after Cheswick is taken away, McMurphy offers Bromden a piece of chewing gum and is given a quiet thank you, revealing that Bromden can both hear and speak. McMurphy suggests they escape the asylum together, but he is taken away and given electroshock treatment. When McMurphy returns to the ward, he shuffles in, bearing a vacant look on his face, but soon laughs and acknowledges that he is playing a joke on the men. Still intent on escaping, McMurphy breaks into the nurses’ office one night and calls Candy and Rose, asking them to bring liquor. McMurphy invites Bromden to leave with him, but Bromden declines. When Candy and Rose arrive, McMurphy pulls them in through a window and awakens the men for a farewell party. Afterward, McMurphy prepares to leave with the women and says goodbye to each of the men. Noting that Billy is upset, McMurphy invites him to come along, but Billy believes he is not ready for the outside world. Realizing that the virginal Billy is attracted to Candy, McMurphy arranges for them to have a private “date.” While waiting for Candy, McMurphy falls asleep and when the orderlies and nurses arrive the next morning to discover the disheveled room, it is too late for him to escape. When the hospital attendants discover Billy in bed with Candy, Ratched asks him if he is ashamed of himself. Billy answers without stuttering that he is not, but when Ratched threatens to tell his mother, he breaks down and is taken from the room by the orderlies. Shortly after, Billy commits suicide. Angry, McMurphy grabs Ratched by the throat and strangles her, until Washington knocks him out. Later order is restored and Ratched, now wearing a neck brace, regains control of the men, although they still play blackjack using cigarettes for money. McMurphy, however, has not been seen and various rumors circulate, some stating that he escaped the asylum and others that he is on another floor, “meek as a lamb.” During the middle of the night, McMurphy is returned to his bed by orderlies. Bromden goes to him, ready for the two of them to escape, but discovers that McMurphy has been given a lobotomy that has left him vacant and spiritless. To free him, Bromden suffocates his friend with a pillow. He then goes to the tub room, lifts the washing station and breaks the window, through which he leaves the asylum.