Celestine (Jeanne Moreau) has a new job as a chambermaid for the quirky M. Monteil (Michel Piccoli), his wife and her father. When the father dies, Celestine decides to quit her job and leave, but when a young girl is raped and murdered, Celestine believes that the Monteils' groundskeeper, Joseph (Georges Geret), is guilty, and stays on in order to prove it. She uses her sexuality and the promise of marriage to get Joseph to confess -- but things do not go as planned.