Laini Taylor, and I very much enjoyed it. The book is subtitled "A Melodrama" which is completely perfect. It's set in the early 20th century, and a young orphan girl named Maud really, really, really wants to be adopted. But getting adopted turns out to be just a smidge different from what she was hoping or expecting, because she's been adopted by Miss Hyacinth and her sister. Miss Hyacinth is, shall we say, a little bit INSANE! She forces Maud to be ah hidden child (I wonder if she perchance read any Margaret Petereson Haddix...)
Anyway, poor Maud is basically a prisoner. But poor Maud is also very fiesty and clever, and it's a joy (and sometimes a fright) to watch her figure out what to do. For me the story went on just a teensy bit too long, but sometimes I attribute that to the audio version because I can't fast forward myself through any parts, and there's certainly enough action that I was not ever bored with the story.
I'd recommend this for middle school girls.