Sublime. There was almost nothing I didn't like about this book. The pacing and mystery really drew me in. I found I empathized with the protagonists, and I constantly wanted to see what happened next.
The star of the show, though, was the circus. More so than in any book I've read since [b:The City and the City|4703581|The City & the City|China Miéville|https://i.gr-assets.com/images/S/compressed.photo.goodreads.com/books/1320475957l/4703581._SY75_.jpg|4767909], the setting was the best character. Ms. Morgenstern's descriptions of the circus were so detailed and compelling (helped by judicious use of the second person point of view) that I couldn't help but feel like it was a real place (that I must visit).
Go read it.