The eccentric Comtesse de Saint-Plâs sells a black Citroën DS to car dealer Paul Souflé. He sells it to the young mathematics teacher Jacques Denzac who is about to marry.

Hélène and François are a perfect couple happily married for twelve years. But Hélène discovers psychoanalysis via a very handsome Dr. Kougloff, and he convinces her that the apparent well-balanced nature of her husband is in fact a cover for horrible tragedies.