The Palazzo Grimani in Venice
Gennaro and his friends, including Orsini, celebrate on the brightly lit terrace, in front of which lies the Giudecca canal. The friends' conversation turns to Don Alfonso, Duke of Ferrara, to whose house they will be travelling the next day, and to his wife, the infamous Lucrezia Borgia. On hearing Lucrezia's name, Orsini tells of how Gennaro and he, alone in a forest, were warned by a mysterious old man to beware her and the entire Borgia family, and that the two of them would die together (Nella fatal di Rimini). Professing his boredom with Orsini's tale Gennaro wanders off and falls asleep nearby. His friends are invited to rejoin the festivities, and he is left alone. A gondola appears and a masked woman steps onto the terrace. She hurries over to the sleeping Gennaro and observes him with affection. (Com'è bello! Quale incanto in quel volto onesto e altero!) She kisses his hand, he wakes and is instantly struck by her beauty. He expresses his love for her and sings of his childhood as an orphan brought up by fishermen. He adds that he loves dearly the mother he has never met. (Di pescatore ignobile esser figliuol credei.) The others return and instantly recognise her as Lucrezia Borgia, listing in turn the members of their families she has killed to Gennaro's horror.