Based on a play Au diable la vertu tells the stories of an unfaithful husband ,Pierre Montabrel, and of an astute burglar, Robert Trémieux.As Pierre needs an alibi he asks a private detective agency to find an alibi and Mr. Tellier, strange private detective finds fast his alibi, Mr. Robert Trémieux.Pierre Montabrel manages to calm his wife Gisèle presenting her Robert Trémieux as an old school friend.But the peace will be short, a police inspector has arrived at Pierre's house for a burglay case in which Robert Trémieux is involved.Till here the story is quite simple.Then begins the meeting with the instructing judge, one has an alibi, the other has another alibi,Miss Véronique de St-Hilaire, victim of the burglary testifies against Pierre, Jacques Lambert, the associate is involved in the case,his girlfriend too .Many characters, many stories, lies and rectifications produce a great confusion in this film.