I'd give this 4.5 stars -- At first the book started out kind of slowly. There were a LOT of unanswered questions which I was anxious to get the answers too. Once it started to pick up, I couldn't stop reading. It was really interesting to figure out all the answers they needed. The one thing I couldn't get over was the description of the Grievers. How in the world do you come up with a half creature/half machine like that? Weird. I'd like to hear a follow up on what those actually are in a future book!