Tony "le Saint-Étienne#Demographics" has served a five-year prison term for a jewel heist and is out on the street and down on his luck. His friend Jo approaches him about a smash-and-grab proposed by mutual friend Mario in which the threesome would cut the glass on a Parisian jeweler's front window in broad daylight and snatch some gems. Tony declines. He then learns that his old girlfriend, Mado, took up in his absence with gangster Parisian nightclub owner Pierre Grutter. Finding Mado working at Grutter's, Tony invites her back to his rundown flat. She is obviously well-kept, and Tony savagely beats her for being so deeply involved with Grutter. Tony changes his mind about the heist; he now accepts on the condition that rather than merely robbing the window, they will take on the more difficult but more lucrative task of robbing the store's safe. Mario suggests they employ the services of Italian compatriot César, a safecracker. The four devise and rehearse an ingenious plan to break into the store and disarm its sophisticated alarm system.