Unholy

Unholy is the last novel of The Haunted Lands trilogy by Richard Lee Byers.

"Forces undreamed of even by Szass Tam have brought havoc and death to Thay, but the lich's true intentions remain a mystery—a mystery that could spell doom for the entire world."

"The formerly green fields lie in war-torn ruins. The formerly living populace in undead. And the formerly brilliant necromancer, the mastermind behind the civil war that drove the ruling council into exile, appears to have gone insane. But rumor spreads of a reason behind his randomness - a reason all survivors of Thay must rally against. "