I ended up staying up late to finish it last night. Thoroughly enjoyed! My feeling about what Verity was doing was mostly accurate, but I didn't at all expect the denouement.
It's books like this that make me annoyed when people criticise Young Adult fiction, or say people shouldn't read it. It's a good book! Accessible to teenagers, but not infantilised or preachy or overly romanticised. Why shouldn't adults read that sort of book?