Randle Patrick McMurphy (Jack Nicholson) is a petty criminal commited to an insane assylum because the prison authority believe he is disturbed. McMurphy's energy and zest for life infects the other men on the ward which infuriates the iron-clad head nurse Mildred Ratched (Louise Fletcher). Life on the ward becomes a battle between McMurphy and Ratched for control over the destinies of the inmates. Most of the men are there by choice and are afraid to leave the comfort of the quiet and controlled ward. McMurphy tries to show them they can have control over their own lives and successfully make their own choices at the same time as Nurse Ratched poisons their souls and undermines their independence. In the end, Nurse Ratched's insidious evil is unrecognizable to the authorities.