Simon, a 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 Promenade de la Croisette, in Cannes, they find the shop of a beautiful antiques dealer (Françoise Fabian) who befriends the group.