When a young couple (Cillian Murphy, Thandie Newton) decide to take a vacation in the wilderness, a secluded cabin located far from the reaches of civilization seems like the perfect location. But things turn sour when a crazed, injured soldier shows up at their door, claiming that a virus is sweeping through a nearby city and is headed their way. With no access to the outside world, there's no way to know if the man is telling the truth, and whether he's motivated by a real plague, by insanity, or by something even darker.