Viclinda and Giselda are concerned about Pagano and his supposed reformation. Arvino asks them to watch his elderly father, Lord Folco, who is spending the night in Arvino's chambers. Giselda prays (Aria: "Salve Maria" / "Hail Mary!"). Pirro and Pagano and their assassins storm the palace. Pagano draws his sword and enters Arvino's chambers. He emerges with a bloody sword and with Viclinda in his custody. Arvino suddenly appears and Pagano is shocked to learn that in the darkness he has killed his father, not his brother ("Orror!" / "Horror! Dreadful monster of Hell..."). A throng calls for Pagano's death, but Giselda protests against more bloodshed. So Pagano is once again sent into exile.