Elena, the wife of Marin Faliero, Doge of Venice, is continually subjected to attacks on her reputation by the patrician Steno whose advances she has rejected. Steno then insults Israele Bertucci, the chief of the Venetian Arsenal in front of his workers. Steno is punished for these offenses, but Faliero is infuriated by the leniency of the punishment. Israele convinces Faliero to join a conspiracy against the Council of Forty, of which Steno is a member.
Meanwhile, Elena is in love with Faliero's friend Fernando, who wants to leave the city to save her from dishonour. During a masked ball, Fernando challenges Steno to a duel for having insulted Elena once again. When Fernando is found dying in the place where the conspirators were to meet, Faliero vows to avenge his death.
The conspiracy collapses following a betrayal by one of its members and the Doge is condemned to death. Before his execution, Elena confesses her love affair with Fernando to him. Faliero begins to curse her, but sensing that his death is imminent, pardons her instead. Faliero is led off. Alone on the stage, Elena hears the sound of the executioner's axe, screams and faints.