The Zombie Chronicles, Book 3: Apocalypse Infection Unleashed Series

When Nick and Dean chase Tahoe into a city where he's taken refuge, they learn that this city is more bizarre and mysterious than they ever thought before. Ignoring their instinct to leave, they put on a brave front and continue their search for Val who has turned into a zombie...and is out on the loose. Dean feels they're closer than ever to getting the vials back, but when he learns about a deadly secret the city hides, his mission turns into a life and death struggle...literally.