Un meurtre a été commis

Commissioner Thomas simultaneously investigates the actions of an oil company, a theft and an assassination, and the kidnapping of a child with look-alikes.

Robert Vernier is assigned by the Secret Service to unmask a band of gangsters determined to get their hands on the plans for a new plane. They manage to steal part of it and kidnap Robert's fiancée, named Monique. Robert will manage to dismantle the gang and will be surprised to find that at the head there is a policeman...

Jacques Hélian, an attractive charm singer, too stifled by the jealousy of the radio director's niece, flees with his orchestra, on the advice of his secretary Bob. They fail in a small village, where there is a boarding school for young girls. Bob responds to the love letters the teacher sends to the handsome singer.

A group of political exiles conspire in France against their government. They are pursued by Daminoff, head of the intelligence service of the country of origin of the conspirators, who uses Nadia, a singer who soon betrays him by taking up the cause of his compatriots. Dramatic chases ensue until Daminoff, having tracked down Nadia and her friends, fires on Chief André and seizes the secret plans. But these are false. André, injured, is stricken with amnesia. Seeing Nadia again, he will become himself again and marry her.

Pursued by a rival gang after a violent robbery, Toni escapes with nearly thirty million francs. On the train to Paris, to avoid arousing suspicion, he has no choice but to threaten an honorable philosophy professor, Justin Mignonnet, with his gun, so that he will carry the loot for him. To make sure he returns the money, he takes his papers and makes him promise to be present at the exchange appointment at the Pigalle Hotel the next day. Completely lost, Mignonnet decides to obey orders, but just as he is about to return the money, a young woman, a member of the enemy gang, comes to collect it.