The Boy Merlin: Red Dragon, White Dragon

On Connan's land in Carmarthen, and against his wishes, Vortigern is building a great tower. Despite countless sacrifices by Grimbald, Vortigern's court magician, the tower keeps falling down. Iefan, a nobleman of the court, is summoned to bring Merlin to Carmarthen; but Merlin's life hangs in the balance when Grimbald calls for another sacrifice — the blood of a fatherless son of a princess...