Something has gone terribly wrong at research station 320, a secret research facility one mile beneath the earth's surface. All communications are gone, all means of escape destroyed and an extremely dangerous horde of rapidly mutating ancient flesh eating creatures are consuming everything in their path. Eight survivors of the outpost, two research subjects, three mercenaries, two research technicians and a medic barricade themselves inside a remote area of the facility with little food, almost no means of defense and little hope of rescue. Their one possible escape route is through thirteen levels of terror that will lead them to the surface. And one of them is not who they seem to be, but the darkness itself which has taken human form.