The marquis of Conchiglia has fallen in love with Cecchina who is a maid. Shocked by the social impropriety of such a match, Cavaliere Armidoro, the fiancee of the marquis's sister, refuses to marry Lucinda. Distraught over losing the man she loves, Lucinda begs the marquis to stop seeing Cecchina. Meanwhile Cecchina has several problems of her own, including Mengotto, a poor man who is enfattuated with her and won't leave her alone, and Sandrina and Paoluccia, two jealous maids who try to cause as much trouble for Cecchina as they can. After many plot twists, the opera ends well when Tagliaferro, a German soldier, reveals that Cecchina is in fact the daughter of a German baron, which enables Cecchina to marry the Marchese without upsetting Armidoro.