Appointed public prosecutor in a small provincial town, Gérard Latour befriends Delanglade, whose young wife becomes his mistress. Shortly afterwards, a fire ravages Delanglade's factory. During the ensuing investigation, the Public Prosecutor discovers the troubled past of the industrialist and his front man, Jacques Perthuis, an ex-convict. They themselves set fire to the factory to collect the insurance premium. Gérard Latour, suspecting his mistress of complicity in her husband's machinations, leaves her after a stormy argument.