A castle can be made safe from the undead, but not from the people inside the walls.
It is seven months since the outbreak. In the anarchy and chaos that came with the undead, civilization was destroyed. In the wars that followed, the planet was nearly ruined. Billions died. Only a few thousand survived.
Fifty people have found refuge in the Tower of London. Zombies plague the city outside the old fortress. The wasteland beyond is filled with nothing but radioactive ruins. With nowhere left to which they can retreat, and in a final attempt to make the ancient castle a place where they can do more than starve, the survivors search for food in the abandoned coastal farms. They find something else. They discover that hunger, thirst, and the undead aren't the only threat they face.