In 1937, in Marseille, Louis-César is an antique dealer who admires Louis XVI and, like him, knows how to pick a lock. At night, he claims to go to a club and becomes a burglar who, for the sake of honesty, only robs trifle things like a rubber, glasses, etc. His sole challenge is to manage to pick the locks and to leave a card with his nickname "Sesame". One night, his wife Élise, that he calls Marie Antoinette, goes to bed but his daughter Annie admits that she found out about his activities and he reluctantly accepts to bring her along in M. Vinières's apartment. He manages to open a safe with a tiara inside. Annie tries it on. As they hear a car coming, they escape. Only when they return home do they realize that Annie still has the tiara on her head. He hides the tiara in an armor in his shop and decides to stop breaking in houses after he has returned it to its rightful owner. Annie flirts with a shy young customer called Jean-Pierre. When Louis-César returns to M. Vinières's ...