[Fizban]

I'm not sure exactly how long ago I read this book but it has been a few years at least.

The parts of the story I remember are that an aristocrat vows to marry the next single woman he meets (I think after being jilted). That person happens to be a singer at a theatre and she was raised genteely and her younger brother has a minor title (I think, or maybe it's just that he inherited a really rich estate). She agrees to marry him if he will save her ill brother, whom she suspects their uncle of trying to see that he doesn't recover from his illness so the uncle can inherit.

They get married and to make it look like a love match, when she's singing on stage, she sings a beautiful love song to the box he's sitting in and he drops a rose down to her. After a few days of this, he departs to get to her brother, whom he finds extremely ill (I believe it was poison but not sure) and he steals him from the uncle and then has to hole up somewhere to nurse him back to enough health to make it to London.

While he is gone, she continues to sing to his empty box as "proof" of her love. One night she is astonished when a rose is dropped and it's her husband's father, giving silent approval.

That's all I recall, I'm afraid. Can't narrow down the names or anything but would really like to re-read this title if I can locate it.