In Book 4, the readers sees what has happened inside the Dupont Federal Center (DFC) and there is some more background on what happened in Idaho Falls. A new character, Captain Angelina Brandon, is tossed into the mix when Sergeant Hathaway and Corporals Valdez and Axtell stumble upon something strange outside the DFC.
The Safeguard group gets to know each other a bit better following the events that happened in Book 3. One member of the group has some issues with what happened in Clovis and feels that they should have done more to help the citizens.
Peter Larkin, Leesa Tobias and Arthur Higgins settle in at Sandhurst. But all is not pleasant in the aftermath of an incursion by the infected.
Firebase Cascade sends the survivors of ODA-141 on a mission to find the source of the infection.
Hathaway, Axtell, Valdez and Brandon are now in the rural areas of Wyoming and facing down winter with limited supplies.
Shark Platoon, now in the DARPA facility in the middle of the Nevada desert, receives orders to join up with other military units as the search for the source of the infection continues.
Jimbo, Melody, Berg and the Kennedy's make an interesting discovery.
The book ends with a combined strike team make up of Rangers, ODA-141 and the SEALs of Shark Platoon enroute to their objective.