- 1790 - Opera buffa Ferrando and Guglielmo (two officers) claim that their fiancées (Dorabella and Fiordiligi, respectively) will be eternally faithful. Don Alfonso joins the discussion and lays a wager with the two officers, claiming he can prove in a day's time that these two women (like all women) are fickle. The wager is accepted: the two officers will pretend to have been called off to war; soon thereafter they shall return in disguise and attempt to seduce each other's lover. The scene shifts to the two women (they are sisters) who are praising their men. Alfonso arrives to announce the bad news: the officers have been called off to war. Ferrando and Guglielmo arrive, brokenhearted, and bid farewell. As the boat with the men sails off to sea, Alfonso and the sisters wish them safe travel, then Alfonso, left alone, rails against the fickleness of women.
Scene 2: A room in the sisters' home
Despina, their maid, arrives and asks what is wrong. Dorabella bemoans the torment of having been left alone. Despina mocks the sisters, advising them to consider new lovers over old lovers. After they depart, Alfonso arrives upon the scene. He fears Despina will recognize the men through their disguises, so he bribes her into helping him win the bet. The two men then arrive, dressed as mustachioed Albanians. The sisters enter and are alarmed by the presence of strange men in their home. The Albanians attempt to win over the sisters, Guglielmo going so far as to point out all of his manly attributes, but to no avail. Ferrando, left alone and sensing victory, praises his love.
Scene 3: A garden
The sisters are still pining. But Despina has asked Don Alfonso to let her take over the seduction plan—and suddenly, the Albanians burst in the scene and threaten to poison themselves if they are not allowed the chance to woo the sisters. As Alfonso tries to calm them, they drink the poison and pass out. Soon thereafter, a doctor arrives on the scene (Despina in disguise), who, through use of a large magnet, is able to revive the Albanians. The revived men, hallucinating, demand a kiss of the goddesses who stand before them. The sisters refuse, even as Alfonso and the doctor (Despina) urge them to acquiesce.