At the end of the last book, Plum Island was attacked and the Variants captured Dr. Lovato thus putting humanity's last hope in jeopardy. Kate was working on a new Variant killing weapon, Kryptonite, and Plum Island was the key to that weapon being ready on time. Of course Master Sergeant Reed Beckham is not going to stand around while the woman he loves is taken to her death by a bunch of mutants so this book starts off right in the action with a rescue mission that is a race against time.

Rescue mission aside there is still a need to deploy Kryptonite as soon as possible but some disturbing information is indicating that it may already be too late. Initial tests have shown that it is very effective against the orginal Variants but there remains no evidence that it will work on the next generation Variants, also known as Juveniles. These new 2nd generation Variants have already evolved into a threat far larger than their parents and their numbers continue to grow at an alarming rate. The struggle for survival continues as humanity fights a war on multiple fronts and the series comes to a thrilling conclusion (of a sort) before this one is over. 

The comments from Nicholas Sansbury Smith at the end of this book indicate that he was happy with his ending and was putting this series aside to work on his Helldivers series next. He did eventually return and continue the series but you could certainly consider the remaining books optional if you want to. The audiobook version once again has Bronson Pinchot at the mic and his performance remains solid.