The adventurer Jeanne de Valois-Saint-Rémy, descendant (by the left hand) of the king of France Henri II, and who claims to be "Countess de la Motte", imagines a tortuous plan to steal a magnificent diamond necklace that the queen Marie-Antoinette refused to buy from the jewelers Boehmer and Bassange.

A woman disappears after visiting her daughter and realizing her presence was unwelcome by her in-laws. Some time later, a body is found in a nearby lake.