Plague by Michael Grant is the fourth book in the Gone series.
This series has a premise that sounds like it was created by a couple of fourteen year old boys in their bedrooms. The kids are in school when suddenly all the adults disappear and the town is enveloped in a large bubble. The kids have to figure out their own society but to complicate things some of the kids start developing magic powers including some of the kids at the reform school down the road some of which are EVIL resulting in many battles and lots of fighting. It's totally absurd which makes it perfect for teenage boys.
In Plague things have gotten bad in the FAYZ. The town is running out of water, there is a horrible flu going around and the most disgusting bugs that eat kids from the inside out are outside the city. Albert sends Sam and a few other kids off to go look for water and then the unthinkable happens. Drake and his horrible whip hand escapes. This leads to a book filled with action and death and lots of gruesome fights.
This book continued along the same line as the previous books in the series. It's a fun read with a lot of action. The book bounced back and forth between characters less often than the previous series. There were some parts that were hard to follow, the giaiaphage/Drake/Brittany storyline was a little confusing and odd but the majority of the book was interesting and engaging.
Appropriateness: This series is perfect for teenage boys. It's sick and twisted and extremely violent. The violence is gruesome the kids kill each other and some of the characters even relish the idea of torturing and killing other kids. The kids drink alcohol to excess and there's a sexual relationship between a couple in this edition, and group of kids display some very hateful and racist behavior. However, there are consequences both physical and emotional to all of the negative behaviors and none of them are glamorized. I wouldn't give this book to a nine year old but it's absolutely appropriate for the12 and up audience that it's targeted towards and this is a series that boys will enjoy.