On the brink of humanity's extinction, Nikola Tesla and a mysterious order of scientists known as the Tellurians revealed a bold plan to save a world ravaged by a disease that turned sane men into ravenous werewolves: the uninfected would abandon the Earth's surface by rising up in floating salvation cities, iron and steel metropolises that carried tens of thousands of refugees above the savage apocalypse.

Twenty years later, only one salvation city remains aloft, while the beasts still rule the world below. Time has taken its toll on the miraculous machinery of the city, and soon the last of the survivors will plummet to their doom. But when Elijah Kelly, a brakeman aboard the largest of the city's Thunder Trains, is infected by the werewolf virus, he discovers a secret world of lies and horrific experiments that hide the disturbing truth about the Tellurians.

When the beast in his blood surges forth, Elijah must choose between the lives of those he loves, and the city that is humanity's last hope of survival.