Ferrando and Guglielmo are on holiday with their fiancées, sisters Dorabella and Fiordiligi, at the Skyline Motel near the Pleasure Garden. Late Friday night in a nightclub, their new friend Don Alfonso makes a bet with Ferrando and Guglielmo that the two sisters, like all women, are not to be trusted. The boys defend their fiancées and accept the challenge. Don Alfonso, with the boys’ co-operation, reckons he can prove his point over the course of the weekend.
On Saturday morning, the Don finds Fiordiligi and Dorabella strolling on the boardwalk, and tells them that their lovers are being called away to war. After saying goodbye and waving the boys off, the girls are inconsolable.
The next morning Despina, a maid in the motel, tries to encourage the girls to enjoy their freedom. Don Alfonso bribes Despina to help him introduce the sisters to two ‘infatuated young friends’ of his, who are in fact Guglielmo and Ferrando in disguise. The sisters are outraged, and refuse to listen to any declarations of love from the disguised boys.
Don Alfonso has another plan. The young men pretend to take poison in order to gain the sisters’ sympathy and Despina, disguised as ‘Doctor Magnetico’, revives them with her famous vibration machine. The sisters help Despina to revive the boys, who renew their flirtatious attack by demanding a kiss. Their advances are again refused.
Interval of 20 minutes
Despina chastises Fiordiligi and Dorabella for not knowing how to deal with men.
The sisters decide that perhaps Despina is right – there can be no harm in amusing themselves with the handsome strangers. They choose which man they’d like.
Don Alfonso brings the girls into the Pleasure Garden to meet the boys again. In the fairground, Dorabella responds quickly to the disguised Guglielmo’s advances. She accepts a gift and relinquishes her locket with Ferrando’s portrait. Fiordiligi, however, refuses to yield to Ferrando, although she admits to herself that her heart has been won. She condemns Dorabella for her betrayal and resolves to leave the Pleasure Garden and join Guglielmo, her fiancé, at the front.