The play is set in the Kingdom of Naples. Montalto, the King's favourite, wants to secure his influence by marrying Theodosia, the sister of the King — which means that he must frustrate the proposed marriage of Theodosia to the Duke of Florence, the brother of the King's late queen. Montalto arranges a hunting party for the King and Duke, which pauses, by plan, at the country house of the noble widow Simphorosa. Montalto's plan is that the Duke will fall in love with Domitilla, the charming, fifteen-year-old daughter of the house. And to that extent his plan succeeds — the Florentine Duke is much taken with the young woman. Also, Montalto quietly informs the Duke that Theodosia is already privately committed to another — that being himself, Montalto. Still, the Duke hesitates to abandon the sister of a powerful monarch. Montalto informs Theodosia of the Duke's interest in Domitilla; he also hints to Riviero, the Duke's secretary, that Theodosia has already yielded her honor — to him, Montalto. All this plotting comes to a head: the King reproaches the Duke for deserting Theodosia, the Duke complains of Theodosia's compromised honor, and Theodosia clashes with her brother and with Domitilla as well. Montalto tries to keep the mess from reaching him. The only link that can connect Montalto with the accusation against Theodosia is the secretary, Riviero. Montalto uses his power to keep both the secretary and the Duke from the King's presence. The King calls for his favorite; concerned that the rumors about Theodosia's compromised honor are true, the King wants to find some nobleman to marry her to control a possible scandal. Montalto volunteers. The King accepts him, but has a strange plan for showing his gratitude. The King orders Montalto and all his party of supporters into custody, and encourages all and sundry to present their complaints to the supposedly "disgraced" favorite. The royal scheme is that Montalto will soon be restored to favor with all his enemies revealed. But Montalto's plot against the duke, and other crimes as well, are demonstrated, with evidence in the favorite's handwriting. The court is amazed to find that the King still appears to favor his favorite. Montalto is brought back to the court — only to face the accusations of his villainy and to be disgraced and condemned to death. Since this is a comedy, it turns out that a man Montalto is supposed to have had murdered is in fact alive, in disguise; he is Riviero, the Duke's secretary. Montalto's death sentence is commuted to banishment. The subplot involves Domitilla, and her infatuation with the King. The King at first plans to arrange a marriage between her and Montalto; the naive girl misunderstands him, and thinks the King has asked her to marry him. When the Duke shows his interest, she rejects him, thinking herself already committed; but this merely drives the Duke and Theodosia together. The girl's mother, Simphorosa, perceives her daughter's situation and asks the King to help resolve it. The King does so, by asking Domitilla to be not his wife but his mistress. The plan works, and Domitilla, her infatuation broken, becomes affianced to the noble young Octavio.
