Giovanni, recently returned from university study in Bologna, has developed an incestuous passion for his sister Annabella, despite their blood relationship, and the play opens with his discussing this ethical problem with Friar Bonaventura. Bonaventura tries to convince Giovanni that his desires are evil despite Giovanni's passionate reasoning, and eventually persuades him to try to rid himself of his feelings through repentance. Annabella, meanwhile, is being approached by a number of suitors, including Bergetto, Grimaldi, and Soranzo. She is not interested in any of them, however, and when Giovanni finally tells her how he feels (obviously having failed in his attempts to repent), she requites his love immediately. Annabella's tutoress Putana encourages the relationship. The siblings consummate their relationship.