Paul Dupré (José Luis de Vilallonga), an aging Italian industrialist, is found dead after receiving an injection from his nurse, Gina (Virna Lisi). With the aid of a lawyer (Pierre Brasseur), Paul's widow, Catherine (Marina Vlady), convinces a magistrate named Gaudet (Bourvil) that Gina poisoned her late husband. Gina is convicted. But when Gaudet learns that Gina is the true culprit, he must resign from his post as a magistrate in order to save Gina from a life in jail.