Gustavo finds himself betrayed on all sides – Rosimonda has released Faramondo, and his son Adolfo is still stubbornly in love with Faramondo's sister. But Rosimonda is not out of danger, for she is still the love-object of Gernando. Gernando has actually joined forces with a lieutenant of King Gustavo (by name, Teobaldo), persuading Teobaldo to abduct Rosimonda for him. Teobaldo's plans do not stop at this, but he and his men attempt a coup to take Gustavo himself hostage. This sudden turn of events is stopped by Faramondo (who had overheard the entire plot, sent his men to rescue his beloved Rosimonda, and personally stopped the coup attempt). Gustavo embraces his unknown rescuer (whose armour hides his face), and when he realises who had saved him and his daughter, bitterly regrets that his oath MUST be carried out... He must still sacrifice Faramondo in blood-vengeance because of Faramondo's slaying of his son Sveno.