Warlock of the Witch World (Witch World, 5)

Take two parents, both gifted with the power who give birth to triplets, two boys and a girl, who exceed their parents in their gifts of power. This is the story of primarily one brother, Kemoc, who goes to extraordinary lengths to save his sister from the machinations of a dark one who is out to lull her into his full power in order to fight those of the white power who are gathered in the Valley in a last ditch effort at survival. Kemoc is left with a dilemma; Must he slay his own sister in order to save them?