A dangerous prisoner, Jacko Thomas, overpowers his police guard and jumps from a speeding train in the Dartmoor countryside. In the ensuing fight Jacko kills the guard and makes his way to a secluded hotel on the moors where Tredgar is being paid to arrange a safe transit for Jacko and his sister Jean. But Jean as no idea of Jacko's murderous character, and when an ex-policeman and a famous novelist book into the isolated hotel, the scene is set for a series of murders and a shocking climax.