Don Alfonso quarrels with soldiers Ferrando and Guglielmo over the faithfulness of their fiancées, Dorabella and Fiordiligi, respectively. To defend the honor of their women, Ferrando and Guglielmo challenge Donalfonso to combat. In lieu of fighting, Don alfonso offers the gentlemen a wager, contending that he can prove Dorabella’s and Fiordiligi’s inconstancy by the day’s end. The soldiers agree to the wager.

The sisters Fiordiligi and Dorabella muse on the perfection of their lovers. Don alfonso arrives to inform them that Ferrando and Guglielmo have been called to the battlefield and must leave immediately. Ferrando and Guglielmo arrive to say goodbye to the sisters. Before they depart, all four lovers swear eternal fidelity.

The sisters are devastated by their lovers’ departure. Their maid, Despina, instructs them not to despair, as men are expendable. She further explains that it is futile to expect fidelity from men and much wiser to treat them with equal faithlessness.

Don Alfonso worries that Despina will discover and reveal his plot, so he bribes her into helping him redirect the sisters’ affections to two “new suitors.” These new suitors — Guglielmo and Ferrando in disguise — immediately attempt to woo the sisters. Failing to recognize them, Fiordiligi and Dorabella flee their advances. Ferrando and Guglielmo mock Don alfonso on his odds of winning the bet. Don alfonso appeals to Despina for help, and she assures him that the suitors will eventually win the sisters over.

Under Don Alfonso’s instruction, Ferrando and Guglielmo, still in disguise, confront the sisters and threaten to poison themselves if their love continues to be unrequited. They drink the “poison” and “collapse.” The sisters summon Despina, who implores them to give the “dying” men some comfort while she fetches a doctor. The “doctor,” Despina in disguise, arrives and treats the gentlemen with a magical implement. The men “revive” and beg for kisses from Fiordiligi and Dorabella. The sisters exit in a flurry of refusals.

Despina tries to persuade Fiordiligi and Dorabella that accepting the attention they are receiving from the new suitors is in their best interest. The sisters decide there is no harm in amusing themselves by entertaining the “strangers.” Dorabella selects Guglielmo, and Fiordiligi chooses to flirt with Ferrando.

Again under Don Alfonso’s instruction, the men arrange a serenade forthe sisters. Ferrando and Fiordiligi go off for a walk, leaving Guglielmo alone with Dorabella. Guglielmo convinces Dorabella to gift him the locket she wears containing Ferrando’s likeness in exchange for a token of his love. Fiordiligi and Ferrando return, and she continues to reject his advances. Once Ferrando leaves, Fiordiligi asks forgiveness from her distant lover for desiring someone else. Ferrando and Guglielmo confer over the status of their bet, and Guglielmo reveals to Ferrando that Dorabella gave him his portrait. Ferrando then vows to win Fiordiligi.

Dorabella relays her success with her new suitor, as well as her new philosophy on love, to Despina and Fiordiligi. Fiordiligi reacts with disbelief. she decides to disguise herself as a soldier and join Guglielmo on the battlefield, hoping her sister will follow. She is stopped, however, by a “lovesick” Ferrando, still in disguise. Fiordiligi finally confesses her love to him and the two agree to marry. During the double wedding ceremony they share with Dorabella and the disguised Guglielmo, the couples undergo a final test of love, resolution and forgiveness as the fateful wager is won and lost.