Dead-tired, Karen, a young psychiatric nurse, catches the last subway train of the night. Before long, she finds herself trapped, along with a handful of other late-night passengers, fighting for their lives against the murderous zealots of a doomsday cult. Now, as the bodies start piling up, Karen, and the rest of the lucky survivors, must fight tooth-and-nail to stay alive, facing the unknown, and the impending apocalypse. But, at the end of the line, there is no place to go but down.