McMurphy (Jack Nicholson) escapes work on a prison farm by feigning mental illness, but he finds himself in a far more coercive institution than the one he left behind. The other men, both sane and insane, are just like him: they hide in the locked ward from the law, their families, or the despair of their own lives.
McMurphy animates the dull monotony with fractious games, pranks, and excursions, but he encounters stiff opposition from the head nurse, Mildred Ratched (Louise Fletcher), whose system provides her with pills and electroshock to maintain control. When the nurse discovers that McMurphy has smuggled two women into the ward, she threatens to tell the mother of young Billy (Brad Dourif). Billy commits suicide and an enraged McMurphy tries to strangle Ratched. McMurphy is lobotomized and returned to the ward only to be smothered by his friend Bromden, who then escapes.
