 A group of train passengers, including a policeman (Ian Hart) a wanted criminal (Mick Sizer) and an M.O.D. scientist (Harriet Ambrose) are travelling to Sheffield when their train crashes inside a tunnel and a strange gas envelopes them. When they awake, they find that Harriet froze them all so they could survive the giant meteor impact that destroyed the rest of the world. Now, they seem to be the only survivors of the human race in a world overrun with tropical plants and patrolled by packs of man-eating dogs.