McMurphy arrives on the mental patient ward and begins to stir up a rebellion against Nurse Ratched’s petty rules and regulations. A power struggle between the nurse and the patient begins. For a short time, McMurphy seems to be winning but Chief realizes Nurse Ratched is just biding her time.
McMurphy finds out that Nurse Ratched can keep him in the hospital as long as she wants, forever if need be. So he begins to conform to the rules until one of the men commits suicide, disappointed that McMurphy has backed down. Nurse Ratched thinks the war is won and decides to punish the men for their rebellion. McMurphy responds by challenging her power again and the battle is back on.
McMurphy smuggles two prostitutes onto the ward one night and the men have a full-blown party, but they’re caught the next morning. Billy Bibbit commits suicide and McMurphy attacks Nurse Ratched. She goes to the hospital to recover and McMurphy undergoes a lobotomy. Saddened and enraged that a free spirit has been destroyed, Chief smothers McMurphy to death and escapes the hospital.