British creepfest. Two college students (Ladd, Gurney) find a body on the steps of London's Russell Square subway platform but it has disappeared by the time Scotland Yard shows up. Inspector Calhoun (Pleasence) investigates since it's not the first time something strange has happened there. He learns he's chasing the remaining survivor of a long-ago cave-in who has mutated into a cannibal-zombie creature.