Extinction Inferno: Extinction Cycle: Dark Age, Book 2 (Unabridged‪)‬

The government said the Variants were dying off....

That the beasts would be extinct in a matter of years....

That the Allied States had returned to prosperity and freedom....

The government was dead wrong. Deep under the cities, the Variants weren't just hiding, they were breeding. While the human survivors of the Extinction Cycle built outposts and brought back industries, the monsters were building something of their own. Working with human collaborators, they constructed a vast underground organic network to control this new army and launch a blitzkrieg assault across the Allied States. After tunneling under the walls, the beasts managed to overwhelm even the most fortified outposts. Many of them fell within days, forcing the military to abandon bases and retreat. 

But not everyone is on the run. Team Ghost hunts a monster behind enemy lines that could change the tide of war. On the USS George Johnson, Doctor Kate Lovato and her team of scientists seek to understand and tap in to the Variant network while oil tycoon S. M. Fischer and his engineers come up with a plan to help buy time for the remaining outposts. And, at Outpost Portland, Captain Reed Beckham and Master Sergeant Parker Horn investigate a frightening conspiracy involving the human collaborators. 

As the Variant armies surge across the Allied States, those working to stop them realize even desperate measures may not be enough to prevent the total annihilation of their country.