Alliance of Light: Bk.2: Grand Conspiracy by Janny Wurts
It is a time of intrigue, fanaticism and rampaging armies. Distrust of sorcery has unleashed a purge of the mageborn -- none reviled more than Arithon, Master of Shadow. Through clever manipulation of events at the hands of Lysaer, Master of Light, Arithon's very name has become anathema. Now, the volatile hatreds that first spearheaded the campaign against Shadow have overtaken all reason. Those that still stand in Arithon's desperate defence are downtrodden, in retreat and close to defeat. The stage is set for ultimate betrayal.