The Weirdstone of Brisingamen

When Colin and Susan find themselves pursued by strange creatures, they are rescued by a powerful Wizard. He reveals a hidden world beneath Alderley Edge, where ancient knights sleep, bound by a magical stone. This stone, the Weirdstone of Brisingamen, is lost, and dark forces are closing in to destroy its power. The children soon discover they are crucial to its recovery, but can they stand against the formidable Morrigan and her deadly brood?