A bit of a departure from normal Williamsons' fare, but it still has some of their trademarks.
Virginia, who is as you may guess a princess, has just finished telling her mother that she will never marry anyone except her ideal man, Leopold, the emperor of a small country. She's maybe only met him once or twice and it was years ago, but she has followed his career with interest and can't help feeling that she'd rather marry no one if she can't have him. She's pretty sure this will never happen, since even though she's royalty, her family isn't that important anymore and they have no money.
The words confessing her attachment are hardly out of her mouth when a letter arrives for her mother.

Emperor Leopold wants to marry her.

Serendipitous as it may seem, it's not the whole truth. Unfortunately. The truth is, he knows it's his duty to marry. His counselor has fixed on Virginia as an eligible bride, and Leopold has agreed because: A) She's Protestant, B) She's of suitably royal blood, C) He thinks she'll be "moldable", and D) He despises the idea of marrying for money or prestige, and since Virginia has neither, he won't be beholden to her or her relatives.
Virginia refuses such terms. She wants romance or nothing. She persuades her mother and, under assumed names, they visit Leopold's country to see if he can possibly love Virginia for herself. ( )