Under the reign of Louis XV, a French aristocrat, fleeing the lawsuit that had just been brought to him in Marseille for dissolute morals, took refuge in Venice accompanied by his mistress, his wife's own sister, whom he passed off as his legitimate wife. . Frequenting assiduously the Salons de la Cité instead of displaying a discretion more in keeping with his situation, he quickly finds himself confronted with the reproaches of his mistress and the investigations of the Venetian spies.