Overhearing Guiglielmo and Ferrando’s excitement at their forthcoming double wedding, Don Alfonso makes a cynical wager with the two young men that their fiancées, Fiordiligi and Dorabella, are as untrustworthy as the next woman in matters of the heart. Confident of their lovers’ fidelity, the boys accept the bet and, at Don Alfonso’s suggestion, pretend to be called away to war. Disguised, they return and set about trying to seduce each other’s unsuspecting fiancées. At first the girls’ loyalty is unwavering but, encouraged to enjoy the ‘harmless flirtation’ by Despina, their maid who is in on the ruse, their constancy begins to crumble…