Dark forces are taking hold in the kingdom of Camelot: King Arthur struggles to keep his knights in line as they steadily divide themselves into factions; the great Merlin has vanished at the hands of his lover and pupil, Nimue; wizards all over the countryside battle for whatever measures of power they can find. At the center of the maelstrom stands Keira, an innocent girl who possesses the ability to foretell the fate of her world. When Keira is kidnapped from her village home, her mother, Alayna, flees to Camelot and finds Mordred, an enigmatic knight who will ultimately become Keira's greatest champion, Alayna's greatest love, and King Arthur's greatest enemy.

In the long tradition of Arthurian legend, Mordred has been characterized as a buffoon, a false knight, and a bloodthirsty traitor. The Book of Mordred reveals a mysterious man through the eyes of three women who love him.