Humanity is teetering on the edge of extinction, decades after a bio-terrorist attack unleashed a virus upon the world...a virus that transformed the vast majority of the population into vicious, ravenous creatures now called, simply, the "infected". What the bombs didn't destroy, the infected overran; what the infected didn't claim, the living pillaged for supplies. The infected are slowly dying off, starving to death from lack of food. What remains are ruins of cities, monuments to decay and despair, overgrown with trees and weeds. In the midst of a seemingly endless winter, nomadic companions Josh and Penelope, the last survivors of a larger group, share the hope of rescuing others like them and hopefully rebuilding civilization. They must face new and terrifying challenges if they are to survive.