The Coranians have won the war, Kymru is defeated. For Havgan, however, the victory is not complete. Cadair Idris, the hall of the High Kings, remains closed to him. To gain entrance he must locate the Four Treasures—the Stone, the Spear, the Cauldron and the Sword—and bring them to the Guardian of the Doors. Only then can he proclaim himself High King of Kymru.
But the Treasures were hidden long ago, after the death of the last High King. To find them Gwydion the Dreamer must locate a long-forgotten song, and the clues it contains. Following the dictates of the song, he persuades Rhiannon, her daughter Gwenhwyvar, and his nephew Arthur to set out with him on the dangerous quest.
Dogged by Havgan's soldiers they race against time to find the artifacts. But the difficult journey is made even harder by the distrust they have for each other, as well as the necessity to face their own worst fears in order to succeed and gain entrance into Cadair Idris—only to watch helplessly as Arthur risks his life, and his very soul, on the next move in the deadly game.