Valentiniano thanks Ezio for beating Attila in battle. Ezio greets Fulvia, but is met with reserve. Massimo, her father and Valentiano's confidant, explains: the emperor wishes to marry his daughter. Massimo, who has long been waiting to take his revenge on Valentiniano for raping his wife, hopes that encouraging the match will make it easier. Fulvia is horrified by her father's hint that, as Valentiniano's wife, she can easily kill him. She feels torn between love for Ezio, fear of the emperor and her obedience as a daughter. Massimo implies that Ezio's influence could get out of control. Valentiniano, not to be swayed, offers Ezio the hand of his sister Onoria. Ezio refuses, telling the emperor that he loves Fulvia. Massimo's seeds of distrust turn into open rivalry. Fulvia senses that Ezio's life is in danger. Onoria says Fulvia must marry the emperor in the morning. She and Onoria, who loves Ezio too, are rivals. Fulvia is confident that she can overcome all difficulties. ACT 2 Massimo is troubled. He commissioned Emilio to assassinate the emperor but nothing has happened. Fulvia hurries in with news that an attempt has been made on the emperor's life. Her father's cold-bloodedness horrifies her. Valentiniano is shocked by such betrayal: somebody wanted him dead, but he survived. Massimo, hypocritically, offers the emperor his help. Fulvia realises that Massimo has stirred up rivalry between Valentiniano and Ezio in order to cast suspicion on Ezio. She reproaches her father. The emperor, now suspecting Ezio of the attempted murder, has him arrested. Fulvia vacillates between love and duty. The only way she might save Ezio would be to marry the emperor. Onoria, refusing to accuse Ezio of betrayal, demands that her brother speak to him himself. Valentiniano summons Ezio and Fulvia; Fulvia must profess that she loves only the emperor. Fulvia's true feelings are too strong. She confesses her love for Ezio. Valentiniano has him arrested. Fulvia's constancy makes Ezio happy. The emperor and Massimo reproach Fulvia. She threatens to disclose her father's plot. Valentiniano punishes Fulvia by intending to marry her immediately. ACT 3 Onoria tries to placate her brother. She begs him to release Ezio and not anger the people. Valentiniano, pretending he will, secretly orders Varo, Ezio's friend, to kill him. Onoria has proof of Ezio's innocence: Emilio admitted making the attempt on Valentiniano's life, exonerated Ezio completely, revealed that the traitor is a friend of the emperor but has taken the name to his grave. Onoria hears about Ezio's murder from her brother. She curses the emperor, who now has no idea who to trust. Onoria reminds him that he seduced Massimo's wife, making Valentiniano suspect Massimo of being behind the plot on his life. Fulvia, hoping to save her father, claims that it she is the guilty party. Alone, bewildered and exhausted, she longs for death. Massimo has stirred the people up against the emperor, intending to kill Valentiniano himself. Ezio, whose death was feigned, saves the tyrant's life. Valentiniano gives Fulvia and Ezio his blessing and forgives Varo and Massimo.