Gangster (Lino Ventura) with his accomplice (Charles Gérard), prepares to take part in the "first psychological hold-up in the history of crime". Next door to the jewellers of Van Cleef & Arpels, on the Croisette, in Cannes, the find the shop of a beautiful antiques dealer (Françoise Fabian) who befriends the group. The driver and the antiques dealer fall in love. He is friendly but unrefined, she is cultivated and independent, but discovers that talking with Simon shows up her vanity, and she desires a simple and clean love. The hold-up which had been planned for a long time by the driver is shown to be more sophisticated than his methods of seduction.