Borough of Bones (Zone War, #2)

Zone War 2. Ajaya is back in the Zone again - training soldiers to survive the unsurvivable, and using his time inside to hunt for answers of his own. And what he finds reaches far, far outside Manhattan. Human life has been extinguished from the Zone, but what's brewing there is far from satisfied. Racing to contain the danger, Ajaya must protect his own from threats in every direction, both outside and inside the deadliest Borough on the planet.