Hélène and Charles Desvallees, both upper-class residents of Versailles, live a very boring and detached life in their comfortable house, and their only common interest is their beloved son Michel. Every other day, Hélène commutes to Paris and Charles suspects that she might be having an affair. He hires a private detective and a couple of days later, his suspicion is confirmed. The investigator tells him that Hélène is having a love affair with the writer Victor Pégala and delivers a picture of her lover with his address to him. Charles visits Victor at his apartment in Paris and introduces himself as Hélène's husband. He lies by telling him that he has an agreement with his wife to tell him about her encounters. Suddenly,and without warning, Charles hits Victor's head with a statue and kills him, and dumps the body in a lake before returning home. Detectives Duval and Gobet are assigned to investigate and interview Hélène, explaining that Victor is missing and her name is in her address book. When Hélène finds the picture of Victor in Charles' jacket pocket, she destroys the evidence and learns that her husband loves her. But the police inspectors are coming to their house again to talk to Charles!
Source : IMDb