A mysterious Front, originating in Scotland and slowly expanding outward, threatens humanity's existence. In defiancé of the known laws of physics, it only kills humans and is otherwise undetectable. Panic-stricken nations struggle against both the advancing menace and a tide of civil unrest. Desperate individuals must find their own paths, and find them quickly. Although very slow, the Front can be deceptively difficult to escape. Mankind has only a few years to pool its rapidly dwindling resources and save itself from extinction.