Gennaro is drawn to a masked lady. His friends including Orsini insult her, unmasking her as the hated Lucrezia Borgia. She vows revenge. Her secret visits to Gennaro arouse her husband’s suspicions. The Duke sentences Gennaro to death for defacing a Borgia crest; Lucrezia must select the method of execution. Choosing poison she subsequently administers the antidote and facilitates Gennaro’s escape. Lucrezia entraps Orsini and colleagues and poisons them, then discovers the disguised Gennaro amongst them. Spurning her proffered antidote he tries to stab her until she reveals herself as his mother. Refusing aid, he dies. Explaining all, Lucrezia collapses.