This is the final book in Maria V. Snyder's glass trilogy. Loved it! I've had mixed feelings about some of Snyder's other books in this series/world, but this one turned out fabulously. For one, this book had my favorite character out of all six of the study/glass books: Valek, the master spy and assassin. When Valek shows up, you never know who is going to show up where in disguise. Valek trains Opal as a spy in this book, which was a fun twist in the story. I also really loved the way Opal's story ended. It was exactly what I wanted, although it wasn't a conventional ending. The only unfortunate thing about this book is that you have to read all six to really appreciate it, and the first and last are the only two that I really like. They can also be quite frightening and intense at times (there are torture scenes - definitely not my favorite) with some very mature themes. I wish I could recommend this series freely, because it has awesome parts, but I don't feel comfortable doing so. It's too bad, because I loved this book!