Prince Arsace of Corinth and Prince Armindo of Rhodes are seeking Queen Partenope, the founder of the city of Naples, in marriage. A third prince, Emilio of Cumae, is at war with Naples and with Partenope. Partenope is primarily attracted to Arsace. However, she does not know that Arsace has previously abandoned Rosmira, who is disguised as a man named Eurimene, and is trying to win him back. Rosmira confronts Arsace as Eurimene and harasses him for his faithlessness, and demands that he keep her true identity secret. Ultimately, Rosmira/Eurimene challenges her lover to a duel in a court of honour, but her identity is revealed when he demands the condition that they fight stripped to the waist.