Léopold, valet de chambre to the avocat général Maître de Royssac, starts studying the penal code and, during his leave, becomes a judge in a "middle" court. His decisions are recognized as final. Léopold falls in love with Agnès, engaged to the two-faced Doctor Ventoux, who becomes "Le chat" when he plays the gangster. Léopold will help "Le chat" pull off the heist of the century, if he remains free to court Agnès. "Le Chat" doesn't play along. A fight breaks out between Léopold's gang and "Le Chat's" gang. The law must prevail.