In a madhouse, Randle Patrick McMurphy, a smart psychotic man, tries to organize his comrades against the strict rules of head nurse Mildred Ratched, in order to lighten their lives. He partially succeeds, but then, he goes too far and manages to organize a covered party, in the night, introducing alchool, drugs and women. Obviously the participants get all drunk and so are easily discovered. Among them there is a young, very fragile, man, heavily vessated by an oppressive mother. When nurse Mildred rebukes him, saying "What will your mom say when she learns about this?" he's shocked and attempts suicide. McMurphy blames that on the nurse and tries to stranlge her. Because of that and all the trouble he caused, the madhouse staff has him lobotomized. One of his most affectionated followers, unable to stand the sight of the once overenergeting man turned into a vegetable, kills him, out of compassion.