So I read this whole book and I'm pretty sure I missed an installment. I remember the majority of what's mentioned in this one, but not all of it. Maybe I skipped book 3? 
 Anyhow, this is the continuation of the Life as we Knew it series. In this story we see how the world starts to regroup after a near extinction level event. We split off into people who were lucky enough to have spots in the Enclaves and those who weren't. Enclavers have enough to eat, air purifiers, and help in the form of Grubs, those unfortunate enough to not have a spot in the enclave. 
 The story is told from the point of view of Jon. who lives in the Enclave with his step mother and half brother. His mother and sister are grubs, because his family only had three passes to get inside, and they decided to send him. 
 Jon somehow comes to believe that this stroke of luck somehow makes him better than those who weren't able to endure their own place in the Enclave. The book basically follows him coming to terms with the unfairness of this caste system. 
 It was a mildly enjoyable read, not as fun as the first book, but still worth the little time it took to get through. 
 They've left this one off in such a way that it can only be assumed there will be a 5th book, and I imagine I'll read that one, too n