Grail : Book Five of the Pendragon Cycle

Drought, plague, and war have left the Isle of the Mighty battered and its heart, the beloved Arthur, grievously injured - until a secret relic is brought before the dying King; a Holy Grail that heals his wounds and restores his vigor.

But soon evil enters the royal court in the guise of a beautiful maiden; a soulless malevolent force capable of seducing the King's loyal champion, and confounding the sage whom some call Merlin, and carrying the sacred Grail - and Arthur's adored Queen - off into the dark unknown. And now Arthur faces the greatest challenge of his sovereignty: a quest of recovery that must lead the noble liege through the realms of magic and the undead, on a trail that winds inexorably toward a grim confrontation with its most foul nemesis...and his destiny.