In his country house, Filippo and his neighbour Nencio are arranging the marriage of the former's daughter, Sandrina, to the latter. Although she loves Nanni, she pretends to
accede to her father's wishes.
When Sandrina tells Nanni the news, he is hurt and frightened, while Nanni's sister Vespina fears losing Nencio, whom she loves.
Nencio serenades Sandrina, threatening to take her by force if necessary. Furious, Sandrina spurns him, and Vespina emerges to slap his face.
Disguised as an old woman, Vespina tells Filippo that she is looking for her daughter's husband, Nencio. Leaving Filippo and Sandrina horrified, she dons another disguise, goes to Nencio as the emissary of a marquis and tells him that the marquis wishes to marry Filippo's daughter. Nencio confronts Filippo, just as "the marquis" (Vespina again) arrives to explain that because Sandrina is of lowly status she will be marrying one of his servants rather than the marquis himself. Nanni, disguised as the servant, marries Sandrina. Filippo is forced to accept the outcome when the truth is revealed and the opera ends with a double celebration as Nencio and Vespina are married.