Wintertime in the moody, atmospheric mists of East Anglia. Diving into the cold, murky water of a lake, Kit and Joe find an elaborate patten - a Fen word for ice skate. Its return to the surface is not widely welcomed and, as it emerges, the story of how the skate became detached from its owner fifty years ago leads the boys deep into a chilling mystery whose conclusion is yet to be played out. What could have been surging up through the ice that day half a century past that so frightened young Tom Townley? Why has Tom suffered constantly from nightmares and visions of beings who make no noise, but so menacingly watch? Who are they watching now - and why?