Handsome young therapist Vincent Bruce (Warren Beatty) is a war veteran who works at a private sanitarium. Vincent's life gradually becomes unhinged as he falls for Lilith Arthur (Jean Seberg), an attractive, unstable and highly manipulative patient. When Stephen Evshevsky (Peter Fonda), another patient at the institution, also becomes enamored with Lilith, it triggers jealousy and desperation in Vincent, leading to a series of dramatic developments.