As her parents plot her impending marriage, Arabella passes a stranger in the street and is immediately smitten. Later on, at a glittering costume ball, she meets him again, unaware that he is Mandryka, the man her father has intended for her. Meanwhile her sister Zdenka who has been raised as a man called "Zdenko", has been corresponding with the lovestruck Matteo under her sister's name. When Mandryka overhears Zdenko fixing an assignation with between Matteo and 'Arabella' his jealousy threatens the whole arrangement!