By Ellen Kushner.
Somehow I found this book mentioned on Sherwood Smith's site (along with it's predecessor, Swordspoint) and connected it to the ideas "fun" and "appropriate for young adults." Oops.
The story is, for reasons not really explained, Katherine's rich uncle, the Mad Duke Tremontaine, invites her to the city to learn swordsmanship. If he does, he'll cancel the pending suits against her family and pay off all their debts. This might give you an idea of the kind of person he is. Once she's in his power, she proceeds to learn swordsmanship, as promised. However, her time in the city shapes her in other ways, too... it's unclear how much of it was planned by the Mad Duke. He indisputably and unnecessarily drugs her at one point so that she won't disturb him with his lover, even though he leaves her to collapse in the same room. Ugh.
This book is well written, after a fashion (good style), and Katherine's voice narrating in various sections is part of what makes it bearable, I think. However, the flagrant sex (and homosexuality, and sexual "liberation" type themes) make it and its predecessor quite unpleasant. You're not missing anything particularly deep or moving if you skip reading this; there are enough other well-written books in the world. If you don't object to the kinds of the content mentioned above, on the other hand, you might it a delightful read, as the dozens of reviewers quotes (mostly for her several previous books, two of which are in the Riverside universe of this one) seem to attest to.