The story starts with the admission of a new patient, Randle P. McMurphy, to a mental hospital in Oregon. He has feigned insanity and has had himself admitted into the mental hospital in order to escape from his prison punishment of weeding peas. While at the mental hospital, he sees an opportunity to make money from his fellow patients and quickly tries to befriend them.
Nurse Ratched, the head nurse in charge of the ward, carefully watches McMurphy and labels him as a troublemaker. In the first group meeting after his arrival at the hospital, McMurphy notices how verbally abusive the patients are towards one another. Later, when he asks them why they are so destructive, McMurphy is told that Nurse Ratched is in charge and wants them to be at each other's throats. They also warn him that she does as she pleases.
McMurphy, being the innate leader and rebel that he is, decides he will try and irritate Nurse Ratched at every opportunity.
He asks her to switch off the radio, which blasts loudly at all times. Furthermore, he scares the Nurse with the scar by coming onto her. McMurphy makes fun of the hospital rules by brushing his teeth with soap when he is not given toothpaste. He sings too loudly and appears half-naked in front of the Nurse, which really agitates her. He even gets the Doctor to requisition a separate game room for the younger men, against Nurse Ratched's advice.
After the patients have the new game room, McMurphy teaches them to play cards and gamble for money, which is forbidden to the patients. He also tries to get Nurse Ratched to change the television viewing time so that the patients can watch the World Series, but she refuses. When he...