Raymond is prostrate with grief over the death of his sister Agnes, so Theodore plots to disguise himself as a beggar and go to the convent to find out what has become of her. He is taken into the convent, where he hopes somehow that Agnes will somehow hear his voice and recognize him, sending some word of her state. He is disappointed when no word comes. However, as he leaves, an elderly nun, Mother St. Ursula, hands him a basket with gifts.
Theodore takes the basket back to Raymond, where they find a note hidden in the linen cover, stating that they should have the cardinal arrest both Mother St. Ursula and the prioress, so that Agnes’s murder can be requited.
Ambrosio instigates out his plot to rape Antonia. With the magic myrtle he enters her chamber and finds her asleep. He performs the magic rite that will prevent her resistance. He is on the point of raping her when Elvira enters the room and confronts him, promising that she will make his true nature public. Ambrosio has not other recourse but to murder Elvira, without carrying out his true purpose of ravishing Antonia. He returns to the abbey, unsatisfied in his lust and horrified that he has now become a murderer.