|US Cover Artist:||Michael Heslop|
|UK Cover Artist:||Oliver Burston|
Will Stanton visits Wales to recover from hepatitis and meets Bran, the Pendragon and befriends him and his dog Cafall. They seek the Golden Harp and awaken the Sleepers to fight the Dark. The Golden Harp was protected by the High Magic and three men: a Lord of the Dark, Artù, and Merriman Lyon. When they find the Harp, a man, Caradog Prichard, kills Cafall, so Bran and Will go to the lake where the Sleepers sleep and play the Harp. At the end of the book, Caradog Prichard put the Harp in the lake. In this book, the main antagonist is the Grey King.
The Grey King was awarded the 1976 Newbery Medal.
Welsh folklore is an important point in the book.