ACT INaples, late 18th century. Two young officers, Ferrando and Guglielmo, boast about the beauty and virtue of their girls, the sisters Fiordiligi and Dorabella. Their older friend, the cynical Don Alfonso, declares that a woman’s constancy is like the phoenix—everyone talks about it but no one has ever seen it. He proposes a wager of one hundred sequins: if they’ll give him one day and do everything he asks, he will prove to them that the sisters are unfaithful, like all other women. Amused, the young men agree.Fiordiligi and Dorabella think of their lovers, imagining that they will soon be married (Duet: “Ah, guarda sorella”). Alfonso’s plot begins when he arrives with terrible news: the young officers have been called away to their regiment. Ferrando and Guglielmo appear, apparently heartbroken, and the four make tearful farewells. As the soldiers leave, the two women and Alfonso wish them a safe journey (Trio: “Soave sia il vento”).The sisters’ maid Despina complains about how much work she has to do around the house. The girls enter and Dorabella vents her despair (“Smanie implacabili”). Despina refuses to take them seriously: they should simply find new lovers, since men are unworthy of a woman’s fidelity (“In uomini, in soldati”). Fiordiligi and Dorabella are shocked. Alfonso arrives and bribes Despina to assist him, without revealing his plot. Ferrando and Guglielmo enter, disguised as “Albanians,” and declare their admiration for the ladies, each addressing the other’s girlfriend. The sisters firmly reject their advances, Fiordiligi comparing her constancy to a rock in a storm (“Come scoglio”). The men are confident of winning the bet. Ferrando expresses his love for Dorabella (“Un’aura amorosa”), and the two friends leave.As the sisters continue to lament the absence of their lovers, the “foreigners” return, pretending to have poisoned themselves in despair over their rejection. Despina and Alfonso go off to fetch help, leaving the two girls to care for the strangers, who find the situation highly amusing. Despina reappears disguised as a doctor and pretends to draw out the poison with a magnet. When Ferrando and Guglielmo request kisses in order to fully recover, the sisters again reject them, but it is clear they’re beginning to show interest in the strangers.ACT IIDespina lectures her mistresses on how to handle men (“Una donna a quindici anni”) and the sisters agree that there can be no harm in a little flirtation. They decide on their partners, each picking the other’s suitor. Guglielmo, flirting with Dorabella, succeeds in replacing her portrait of Ferrando with his own gift (Duet: “Il core vi dono”). Ferrando has less luck with Fiordiligi, but when he has left, she struggles with her emotions (“Per pieta, ben mio”).Ferrando is certain that they have won the wager. Guglielmo is happy to hear that Fiordiligi has been faithful to him, but when he shows his friend the portrait he took from Dorabella, Ferrando is furious. Guglielmo, adopting Alfonso’s philosophy, blames it on the women (“Donne mie, la fate a tanti!”). He asks Alfonso to pay him his half of the winnings, but Alfonso reminds him that the day is not yet over.Fiordiligi reproaches her sister for her behavior, but Dorabella replies that love is a thief who rewards those who obey him (“È amore un ladroncello”). Alone, Fiordiligi decides to join Guglielmo at the front, when suddenly Ferrando appears. He tries one last time to seduce her and succeeds.Guglielmo is furious, but Alfonso again declares that this is the way women are. A man who has been deceived can blame only himself.The sisters have agreed to marry the “foreigners.” Everything is ready and Alfonso arrives with the notary—Despina in another disguise. As Fiordiligi and Dorabella sign the contract, military music announces the return of their former lovers. In panic, they hide their intended husbands, who return as their real selves, first pretending surprise at their reception, then, when they discover the marriage contract, blaming the girls and threatening revenge. Finally, the men reveal their disguised identities and Fiordiligi and Dorabella ask forgiveness. Alfonso bids the lovers learn their lesson.