During a storm, three travellers take refuge in an inn in the country. Alberto has been betrothed to a woman whom he has never met, and is on his way to meet her. Don Parmenione, accompanied by Martino, is trying to trace a friend's sister, who has disappeared. When the storm is over, Alberto leaves, accidentally taking Parmenione's luggage with him instead of his own. Martino opens Alberto's suitcase and discovers, among his papers, a portrait, presumably of the bride-to-be. Parmenione decides to masquerade as Albert and claim the bride for himself.
At Don Eusebio's house, Ernestina, who has fallen on hard times, agrees to extend her stay and take on the role of Berenice's companion. Berenice, worried about marrying a man whom she has never met, asks Ernestina to pretend to be her. She herself will meanwhile play the role of a maid, so that she can observe Alberto and decide whether she is prepared to marry him. Parmenione, accompanied by Martino, now announces himself as Alberto and pays court to the disguised Ernestina, notwithstanding that she is not the lady in the portrait. The two are attracted to each other.
Alberto himself arrives, and meets the pretended maid, Berenice. A mutual attraction also springs up between these two, but Berenice is disconcerted to learn that Alberto has apparently already arrived and can prove who he is, whereas this man has no papers to identify him. The real Alberto and the imposter each try to convince Eusebio that they are who they say they are, and Berenice, who knows which one she would rather marry, subjects Parmenione to a severe cross-examination. He is eventually forced to admit his deception. Berenice can now marry Alberto and Parmenione can marry Ernestina - who turns out to the woman he was trying to trace, the sister of his friend. And the portrait in Alberto's luggage? It was of his own sister, to be given to Berenice as a wedding-present.