Grail: The Pendragon Cycle, Book 5

Drought, plague, and war have left the Isle of Mighty battered and the beloved King Arthur grievously injured. But astonishingly, the High King lives, his wounds healed by a sacred and secret relic: the Holy Grail. Now, in this time of rampant disease and death, the great king wants to share the Grail's curative powers with all who require it. But with the Grail, evil has entered the royal court, in the guise of a beautiful maiden who seduces the King's most loyal champion. Confounding both Arthur and the sage Merlin, evil abducts the Grail, along with Arthur's beloved Queen, and carries them off into the dark unknown. Now Arthur faces the greatest challenge of his sovereignty: to recover his lost treasures. It will lead him through realms of magic and the undead, on a trail that winds inexorably toward a grim confrontation with his most foul nemesis - and his destiny.