ACT I

Ferrando and Guglielmo discuss the fidelity of women with Don Alfonso. They claim that their own fiancées, Fiordiligi and Dorabella, are immune to any temptation. Don Alfonso insists that all women are unfaithful, and his two friends demand that he prove it. So Don Alfonso challenges them to a wager. He wants to show them both that even their girlfriends are no exception to the rule. The two of them agree to follow Don Alfonso’s instructions for the next 24 hours.

Fiordiligi and Dorabella are waiting for their lovers. But in their place, Don Alfonso arrives to announce that Guglielmo and Ferrando have been called up for military duty at short notice. They are just coming back to say their farewells.

Despina tries to comfort the two women over their loss and urges both Dorabella and Fiordiligi to find new lovers in the meantime. They are shocked at the idea.

Ferrando and Guglielmo return, disguised as foreigners. They remain unrecognized, and now begin to woo the two women. Despina helps them, but their efforts are in vain. The friends are rejected brusquely, and already begin to celebrate winning their wager. But they are too soon, as the agreed 24 hours are not yet over. While Ferrando ponders his love for Dorabella, Despina is preparing the next steps with Don Alfonso, raising the question as to the true nature of love.

The two spurned ‘foreigners’ now pretend to kill themselves. They succeed in impressing Dorabella and Fiordiligi, awakening their pity. The two men are seemingly saved from death by Despina, now disguised as a healer. The women’s display of compassion encourages the men to try another attempt at courtship; this confuses Dorabella and Fiordiligi and they depart, furious. 

INTERVAL

ACT II

Despina shares her own experiences of love’s variety with the two women. Dorabella and Fiordiligi decide to engage with the two men, just for the fun of it. Each already has her own favourite – namely the fiancé of the other. A crisscrossing game ensues. Dorabella responds enthusiastically to Guglielmo’s courtship, while Fiordiligi struggles with conflicting feelings and desperately tries to find a way to preserve her honour and innocence. Guglielmo reports to Ferrando his experiences with Dorabella. Despite her betrayal, Ferrando still feels deeply committed to her, though she meanwhile seems to have taken on Despina’s views wholesale. Ultimately, the despairing Fiordiligi also follows her on this path, falling in love with Ferrando. Don Alfonso sees his beliefs confirmed: ‘Così fan tutte – that’s how all are!’. 

Fiordiligi and Dorabella are ready to marry their new lovers. Despina pretends to be a notary and issues the marriage contracts. The new couples sign them. Don Alfonso now unexpectedly announces the return of the women’s original fiancés. Guglielmo and Ferrando reveal their true identities. The irritation is considerable; the experiment has succeeded, and nothing is how it was before.