It's love at first sight for Arabella and the rich, handsome stranger Mandryka, but Zdenka, in love with one of Arabella's rejected suitors, throws a wrench actually, a room key into the works.
The story is a bit of fluff, its charming characters engaged in a mix-up so contrived it beggars even theatrical suspension of disbelief: The penniless Count and Countess Waldner hope to marry their daughter Arabella to a wealthy man, and since they can't afford to launch younger daughter Zdenka into society at the same time, they have her dress as a boy.