Charles Masson (Michel Bouquet), an advertising executive, is having an affair with Laura, the wife of his best friend, the architect François Tellier. Charles strangles Laura when one of their S&M games goes too far. Dazed, Charles walks out of the borrowed apartment in Paris and soon bumps into François in a nearby bistro.
They drive back together to Versailles, where they have beautiful neighboring houses designed by François. The owner of the apartment had seen Laura and Charles together two months earlier, but she does not tell the police on the advice of François. Even though the police do not seem to have any clues to the crime, Charles has a difficult time coping with the situation, and trying to live a normal life with his two children and loving wife Hélène (Stéphane Audran).