From the introduction:
Four years ago a mysterious virus ravaged the world, turning anyone infected into mindless, flesh eating monsters.
Various groups and communities have sprung up over the nations in an attempt to survive in this hell. Every day is a struggle. Every day people die and the masses of the dead grow larger.
You are part of one of these communities. You are part of the Exploration Corps. You venture out into the world in search of resources. Be it food and water or other survivors or sanctuaries.