Don Alfonso and his young friends Ferrando and Guglielmo are arguing over the fidelity of women. Alfonso insists that all women are fickle, while Ferrando and Guglielmo refuse to believe that their fiancées, the sisters Fiordiligi and Dorabella, could ever be unfaithful. Don Alfonso wagers that by the end of that very day their fiancées will have betrayed them. He instructs Ferrando and Guglielmo to pretend that they have received orders to go off to war........