The Wicked Day (The Arthurian Saga, Book 4)

Far from being the scourge of Arthur, his bastard son Mordred actually strives to resist Merlin's prophecy of doom. But he is thwarted by the schemes of his sorceress mother, Queen Morgause, who has brough him up to be her revenge incarnate, and by misunderstandings beyond his control. Prophecy triumphs, and the confrontation that is as fatal as it is inevitable is played out against the darkened walls of the city of Camelot.