Del McAllen shivered, though it had nothing to do with the cold. He twisted his head, the torch mounted on his  helmet swinging its beam across the walls of the tunnel that had been roughly hewn from the ice, the pool of light twisting and skittering across the frozen surface. There was something wrong here, something he couldn't quite put his finger on.  It was unsettling him.

On a lonely stretch of Welsh coastline a fisherman is killed by a hideous creature from beneath the waves. When the Doctor and Rose arrive, they discover a village where the children are plagued by nightmares, and the nights are ruled by monsters. The villagers suspect that ailing industrialist Nathanial Morton is to blame, but the Doctor has suspicions of his own.