During a plane crash, Professor Sellier, an atomic scientist carrying very important documents, dies and his papers are stolen. Bordy, a sergeant in the Second Bureau, is asked to take Sellier's place in his family's home, in order to make the kidnappers believe that he is not dead.

An unscrupulous young man uses his "fiancée", who haunts gambling halls, to recruit the collaborators he needs to pull off his scams. When these unlucky gamblers are driven to dishonor by debts, he has his fiancée lend them money, and the next day he has them write checks, which of course bounce. All they have to do then is walk straight ahead, her charm encouraging them to do so. But the carefully planned hold-up at the home of a wealthy American tax dodger is a fiasco. The thief finds the safe already emptied by the very man who reported the bargain. But the unfaithful informer is fooled in turn: the loot he was about to take away in an Air-France suitcase is innocently snatched by a group of nuns who take the wrong luggage and unknowingly take off with 500 million dollars.