Riccardo attends a session with the sorceress Ulrica in disguise. She predicts he will die at the hand of the first man to shake his hand that morning. Riccardo laughs. Then he shakes the hand of Renato, his best friend, who has come to find him. Everyone laughs. Ulrica does not.

Amelia goes alone at night to a desolate field to gather a magic herb that, according to the sorceress, will uproot her forbidden love. Riccardo follows her. They confess their love to each other — for the first and only time. Renato arrives to warn Riccardo of a conspiracy. Riccardo flees, entrusting the veiled Amelia to her husband's escort. The conspirators stop Renato and lift the veil. Renato sees his wife.

Renato, beside himself, decides to kill Riccardo. He joins the conspirators. They draw lots to decide who will be the assassin — it falls to him. At the grand masked ball, Amelia begs Riccardo to flee. He refuses: it would be dishonourable. Oscar, naively, points the conspirators to his disguise. Renato stabs him. Riccardo, dying, swears that Amelia was innocent and forgives Renato. He dies.