Ferrando and Guglielmo are convinced of the fidelity of Fiordiligi and Dorabella, the two sisters to whom they are betrothed. Don Alfonso, on the other hand, claims all women are fickle and wagers that he can prove it. The young men agree to take AlfonsoÅLs test, and he tells the sisters that their husbands-to-be have been enlisted into the army. Once the men have departed, the sisters’ maid Despina is persuaded by Alfonso to introduce two young Albanian friends (Ferrando and Guglielmo in disguise) to Fiordiligi and Dorabella. Each "stranger" then begins to court the otherÅLs fianc.e, and they begin to make progress after pretending to take poison. Despina disguises herself as a doctor and [with the Mesmerian magnetic therapy] successfully cures the Albanians.
When Ferrando learns that Dorabella has yielded to Guglielmo, he becomes yet more determined to win Fiordiligi’s heart. Eventually, she too succumbs and a double wedding is planned − with Despina, again in disguise, as the notary. Just as the army is heard returning, the Albanian newlyweds disappear and Ferrando and Guglielmo appear in their place. Producing the marriage contract, they remonstrate with the sisters, who soon confess their deceit. After paying Alfonso his wager, Ferrando and Guglielmo forgive Fiordiligi and Dorabella.