There's always been something in the caves. Over the years people have gone in and not come out. But that was a long time ago. They've been sealed for the best part of a century. Eight hours ago, something changed. Three students somehow found their way in. Now time's running out for them. Their one hope is a man called Rhys Williams. Because somehow, he has a map. NOTE: Torchwood contains adult material and may not be suitable for younger listeners.