The invasion came without warning. Alien forces struck human cities simultaneously, killing millions in the opening hours of what would become an apocalyptic first contact. World governments retaliated with nuclear weapons—a decision that poisoned the environment as thoroughly as the aliens had devastated the population. Now the aliens roam the irradiated wastelands above while human survivors cluster in the city's sewers, subway tunnels, and basements, building makeshift arsenals and planning the counterattack that may be humanity's only remaining option.