Fearing the theft of an important secret formula, the scientist Claude Amory asks for help from Monsieur Préval, director of the Sûreté. But when Amory is mysteriously poisoned inside his own home, the detective realizes the case is more serious than he had imagined and decides to investigate each of the suspects.

The naval officer Maurice de Vergnes, tired of the extravagance of his fiancée Moussia, finds with pleasure a childhood friend: Anna. Jealous, Moussia breaks up with him and Maurice marries Anna. A few years later, Moussia reappears when war is declared. She is now a spy under the orders of Howell... This is a troncated version of a longer film.