Act I

Two young men, Ferrando and Guglielmo, argue about the fidelity of women. The cynical Don Alfonso doubts that women can be constant; Ferrando and Guglielmo refuse to believe that their fiancées, Fiordiligi and Dorabella, would ever betray their faith. Alfonso offers the young men a wager: he will prove that their lovers can be unfaithful, like all other women. The boys defend their fiancées and accept the challenge, agreeing to pretend they have received orders to report for military service.

The next morning Fiordiligi and Dorabella (who are sisters) daydream about their lovers. Alfonso arrives and sets out the deception, pretending that the boys have been called up. Ferrando and Guglielmo arrive and after all say their goodbyes, the girls are inconsolable.

Despina, the sisters’ friend, complains about how much work she has to do. When the sisters return heartbroken, she encourages the girls to enjoy their freedom and find new lovers, but Fiordiligi and Dorabella cannot fathom such a betrayal.

The sisters leave; Don Alfonso, who has overheard the conversation, bribes Despina to help him introduce the sisters to two “infatuated young friends” of his, who are in fact Guglielmo and Ferrando in disguise. When the new suitors make advances toward the sisters, the girls are outraged at these strangers’ presumption and refuse to listen to any declarations of love. The men are confident of winning the bet.

Alfonso has another plan: the young men pretend to take poison in order to gain the sisters’ sympathy. Despina and Alfonso go off to fetch help, leaving the two girls to care for the strangers. Despina reappears disguised as a doctor and pretends to heal the boys. When Ferrando and Guglielmo request kisses in order to fully recover, the sisters again reject them.

Act II

Despina chastises Fiordiligi and Dorabella for not knowing how to deal with men. The sisters decide that perhaps Despina is right—there can be no harm in amusing themselves with the handsome strangers. They choose which man they’d like, each picking the other’s fiancée.

Dorabella responds quickly to the disguised Guglielmo’s advances. She accepts a gift and relinquishes her locket with Ferrando’s portrait. Fiordiligi however refuses to yield to Ferrando, although she admits to herself that her heart has

been won.

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. Gugliemo asks Alfonso to pay him his half of the winnings, but Alfonso reminds him that the day is not yet over.

Fiordiligi condemns Dorabella for her betrayal and resolves to join her beloved at the front.

Ferrando suddenly appears and declares his love for Fiordiligi with renewed passion. While Guglielmo watches helplessly, she finally accepts. Guglielmo and Ferrando are distraught at their fiancées’ infidelity. Don Alfonso encourages the boys to forgive the women and marry them. After all, their behavior is only human nature.

The sisters have agreed to marry the young strangers, and Despina does the honors. Alfonso suddenly announces that Guglielmo and Ferrando have returned. In panic, the sisters hide their intended husbands, who return as their real selves and are horrified to discover the marriage contracts. The boys reveal the entire charade, and Fiordiligi and Dorabella ask forgiveness. Alfonso bids the lovers learn their lesson.