Elly Johnson is puzzled by messages on her bedroom wall. Why had the shadows scrawled the words 'Casket' and 'Seek the Guardian?' Hoping the skulls she and her brother had seen when they had been lost under Dartmoor might give her a clue to solving the mystery, she returns to the tunnels to find them. However, little does she know of the dangers that lie ahead. Does Elly find the skulls? Does she solve the puzzle of the shadows messages? Find out when Elly returns to the dreaded Devil's Cauldron in the heart of Dartmoor.