Così fan tutte
Ferrando and Guglielmo, two young officers discuss the true faithfulness of their fiancées. A cynical old man, Don Alfonso, joins in their conversation and bets them that if they give him one day's time, he can prove to them that all women are fickle. Ferrando and Guglielmo agree to the wager. Sisters, Fiordiligi and Dorabella, the two fiancées, happily compare pictures of their boyfriends when the two officers arrive telling them that they have been called for war. Secretly, they will return in disguise and do whatever Alfonso says. The two women, full of grief, bid farewell to their lovers. Don Alfonso couldn't be any happier as he sees his plan coming to fruition.
Back in the sisters' home, Despina, the maid, consoles the young mistresses. She tells them to forget their lovers and find new ones. Don Alfonso arrives, and fearing that Despina may recognize the disguised officers, convinces Despina to help him win his wager. She agrees and helps introduce the disguised officers as two exquisitely dressed "Albanians." Fiordiligi and Dorabella take no interest in the "newcomers" despite the efforts of Despina and Don Alfonso. After the men leave, they rejoice over their fiancées' faithfulness, but Alfonso reminds them they have a whole day ahead of them.
A while has passed, and Alfonso brings the "Albanians" back to the women, who are now in the garden. The men, feigning sickness, claim to have been poisoned. The women call for Despina's help. She tells them to look over the men while she fetches a doctor. Moments later, Despina returns disguised as the doctor and waves a large magnet over them men's bodies. Suddenly, the "Albanians" instantly regain their health and ask for a kiss from the beautiful young maidens. Though they begin warming up to the "Albanians" they still refuse to give them kisses.
Following the events in the garden, Despina urges the sisters to choose their favorite "Albanian." After agreeing that a little light-hearted flirting wouldn't hurt anything, each sister chooses the other's lover, which goes according to Don Alfonso's plan. The Albanian's return and serenade the sisters. Afterward, Despina and Don Alfonso give them courting lessons before leaving the sisters alone with the Albanians.
In the garden Dorabella and the disguised Guglielmo pair off, leaving Fiordiligi with the disguised Ferrando. Dorabella and Guglielmo seem to hit it off, and before long, they exchange mementos. Fiordiligi and Ferrando do not share the same chemistry as the other couple. Afterward, the two men compare notes. Ferrando is upset that his fiancée has taken to Guglielmo so quickly. Guglielmo consoles him but also gloats of his own fiancée's steadfastness.
Up in the sisters' room, Dorabella admits to Fiordiligi that she has fallen for the Albanian. Upset by her sister's infidelity, Fiordiligi pledges to visit their fiancés on the front lines. Before she is able to depart, Ferrando, still disguised, shows up again, attempting to woo Fiordiligi's heart. She finally gives in and falls into his arms. Guglielmo becomes furious when he learns of his fiancée's actions. Don Alfonso and the two officers agree that he has won the wager, but they still owe Alfonso more time. That evening, Don Alfonso plans for a double wedding.
That night, Despina disguises herself as the marriage notary. Both couples sign their marriage contracts, and all is well until they hear military music in the distance signaling the return of the officers. The women hide their "Albanian" husbands, fearing the return of their fiancés. The two men quickly change into their uniforms and return to the house. Don Alfonso reveals the signed marriage contracts to the officers, and after becoming furious, they leave the house. Don Alfonso then reveals Despina's true identity to the sisters moments before the two men arrive again dressed as both the officer and the Albanian. When the sisters finally learn of Don Alfonso's wager, forgiveness is given all around.