A parasite called "the Devil Worm" (implied to be of extraterrestrial origin) infects most of humanity, turning them into vicious undead mutants called the "Ridden". One year after the beginning of the outbreak, pockets of humanity attempt to survive in the post-apocalyptic world. A group of veteran survivors called the "Cleaners" fight the Ridden and defend Fort Hope, a settlement within fictional Finleyville, PA.
