City of the Sorcerers — Mary H. Herbert

Peace has flourished for over twenty years on the Dark Horse Plains. Under the leadership of Lady Gabria and Lord Athlone, the outcast magic-wielders have gained a tenuous acceptance among their people. But when a devastating plague sweeps over the eleven Clans of Valorian, old suspicions of sorcery flare. The clans' only hope for survival rests with a handful of young magic-wielders and their quest to the ruins of Moy Tura, ancient and feared city of the sorcerers.