Alibi pour un meurtre.

Married to a businessman who neglects her, Laurence cheats on him with Mauliaire, a young actor. Letters and photos of the young woman addressed to her lover are stolen by a blackmailer who demands a large sum in exchange. Distraught, Laurence goes to see Maître Tom Savier and displays such persuasive charm that the lawyer gives in to her demands and decides to get her out of this predicament. But he is soon spotted by the blackmailer. Meanwhile, Laurence disappears. Following a visit to Mauliaire, Tom discovers that the woman he has met is not Laurance, but Lydie Audry, the industrialist's mistress. As for Laurence, her mutilated corpse is discovered at a level crossing. Was it a crime? Accident? Suicide? Inspector Muller is put in charge of the investigation, and his suspicions turn to the blackmailer. After many twists and turns, the real culprit is unmasked.