Well that ending just blew me away!!!! Holy Smokes!!!! If you're into sci-fi, you have got to read this!!! 
 If you've started this book, and you're feeling like it dragging a bit, or if you're confused about why the Wallfacer project was considered a good idea, or if you're wishing some of the characters from the first book were still around, keep reading! It gets better. There's a battle sequence that is one of the most intense things I've ever read, and the ending is superb. The series could have easily ended there satisfactorily; I'm interested to see what is going to develop in book 3. 
 Other reviewers have done a good job of summarizing the plot so I won't do that here. But what I will say is that in addition to some great story telling, this book really gets you thinking about what it means to be human. As I was reading this, I heard a story on NPR dealing with triage during Hurricane Katrina. Doctors and nurses, forced to deal with a shortage of supplies, had to make some really tough decisions about who to save, and in what order people would be evacuated. This book deals with the same type of moral questions, and does an amazing job showing how people think/behave in the face of uncertainty. There were moments that were incredibly dark, but don't give up hope on humanity just yet.