A well respected monk, Capucino Ambrosio compromises himself with his carnal lust for a pupil, a woman disguised as a monk (Matilda), she tempts the monk to transgress and he is soon found desiring another, the innocent Antonia. Matilda uses magic spells to help the monk in his pursuit of Antonia, whom he later rapes and kills. It later emerges that Matilda is an instrument of Satan in female form. Focus also is also shown on Antonia's previous relationship with Lorenzo, whose sister is tortured by hypocritical nuns for her own relationship. Returning to Ambrosio, he is delivered to the Inquisition; escaping only by selling his soul to the devil. The devil prevents Ambrosio's final repentance, and informs Ambrosio that Antonia is the monk's sister.