Michele Morgan plays a reclusive Parisian music teacher. She gets her jollies by peeking through her window and witnessing the romantic liaisons of her female neighbor. When the girl is strangled by one of her lovers, the killer (Simon Andreau) hides out in Michele's apartment. The widow is turned on by the dangerous eroticism of the situation, and soon becomes the murderer's lover. A blackmailer (Claud Rich) extracts a great deal of money from the errant Morgan, whereupon it is revealed that the "murder victim" (Dany Saval) is very much alive and part of the extortion scheme.