The scene is set in the neighborhood of Naples.

Scene I: The curtain rises on a heated argument between two ardent young men – Ferrando and Guglielmo-and the worldly-wise, cynical old Don Alfonso.

Of course, their beloved Fiordiligi and Dorabella are not like other girls, and what did he mean by saying that none of them can be trusted in matters of the heart?

A bet perhaps? But they have to keep the secret and do as they are told during the test period. The bet is accepted.

Scene 2: Don Alfonso enters breathless and agitated. Dreadful news. The young men are called away to their regiment and have to leave at once.

Amid tears and protestations of eternal love, the parting is made with exhortations for a safe journey.

Scene 3: The girls’ maid, Despina, making their morning chocolate has to listen to ardent expressions of despair at separation. Getting tired of it, she advises the girls to amuse themselves in other directions. After all, their young men are away, and they need cheering up.

Don Alfonso and Despina are old friends, and he comes now to seek her help in urging the attentions of two delightful young men recently arrived from abroad. Ferrando and Guglielmo enter suitably disguised, and as the girls return the two men express their admiration-each for the other’s lover.

Horrendous scenes of outraged modesty and assaulted honor are somewhat mollified by Don Alfonso claiming that the two men are old friends and perfectly respectable. Nevertheless, the girls remain firm as rocks in their professions of constancy and, at Guglielmo’s further insistence, retreat in confusion leaving the men convulsed with laughter.

Scene 4: The girls, still inconsolable, are further alarmed by the sudden appearance of the two men, who, protesting their unrequited passions, swallow what appears to be arsenic and collapse in front of them.

Despina and Don Alfonso are dispatched in search of a doctor while the girls give some embarrassed consolation to the inert-but secretly very amused – patients.

Compassion begins to overcome prudery, and when Dr. Mesmer’s disciple (Despina in disguise) effects a miraculous cure through the magic properties of mesmerism the girls find that their obvious relief and concern have served to incite the two men to further protestations of love.

Scene I: Despina continue to urge the girls towards more liberal conduct – there is, after all, no danger.

Left to each other, the girls admit there could be no harm in a little innocent flirtation, and each selects her man. It is clear that they in no way resemble either in looks or character their own absent loves. Nor do they, for they have swapped partners.

Scene 2: The men have arranged an al fresco party for the girls, but, now that a flirtation has become a possibility, it needs the contrived efforts of Don Alfonso and Despina.

Guglielmo makes his protestations to Dorabella, and to his astonishment finds that she soon yields and consents to exchange lockets as token of their new love.

Ferrando does not fare so well with Fiordiligi. She dismisses him abruptly and only when alone confesses the strength of her new feelings for him, asking her distant lover to forgive her faithlessness.

When the two young men meet to compare notes, Ferrando is overcome with despair when his friend produces Dorabella’ s locket and tells of her unfaithfulness.

Scene 3: Don Alfonso and Guglielmo hide to watch Ferrando’s final assault on Fiordiligi’ s constancy. She confides her new love to Dorabella, who urges her to yield.

But Fiordiligi is still afraid. Ferrando surprises her and at last her resistance fails – to the extreme anger of Guglielmo and the delight of Don Alfonso. He has won his bet.

Scene 4: The wedding of the new lovers is under way. The old notary (once again Despina in disguise) reads the marriage contract but, at the moment of signature, a roll of drums announces the return of the army.

The two men rush off and barely manage to return as their former selves in time to catch the girls at their wedding feast.

Deception is at an end. Disguises, tricks, wagers, failures and frailties are confessed, and there is nothing for it but for the lovers to follow Don Alfonso’s advice to forgive each other and try to make amends, all a little wiser for the lessons learned and the wager lost.