The foreign princes, Amida and Ormindo, who are assisting in the defense of Mauretania, are both in love with Erisbe who is unhappily married to Hariadeno, Mauretania's elderly king. The princes agree to remain friends while they test her love. During the course of the opera, there is much plotting by Amore, Princess Sicle (Amida's abandoned lover) and Erice (Sicle's nurse) to interfere with the contest. Erice stages a séance to communicate with the 'dead' Sicle who reproaches Amida for his inconstancy which had driven her to suicide. Amida, overcome with remorse, realizes that he still loves Princess Sicle and is overjoyed when it is revealed that she is actually alive and not a ghost. Meanwhile, Erisbe and Ormindo decide to elope to Tunis, where Ormindo must defend his homeland from attack. When King Hariadeno discovers their adultery, he orders his captain, Osmano, to have them poisoned. However, Osmano substitutes a sleeping potion for the poison at the urging of Mirinda (Erisbe's confidante) who has promised to marry him if he spares the lovers. All ends more or less happily when the King learns that Ormindo is actually his son from a youthful liaison. He forgives everyone and cedes his kingdom to Ormindo.