Unclean

Unclean is the first novel of The Haunted Lands trilogy by Richard Lee Byers.

"The realm of Thay has long been ruled by the uneasy peace of an alliance of wizards, but all along there has been one who believes he is the true master. And when that one wizard finally moves against his former allies, his homeland could be only the first of his conquests."

Summary
Unclean begins multiple story lines. The first is that of Bareris Anskuld, a bard returning to Thay after a period of time away trying to earn riches so that he and his love, Tammith, can live comfortably. Unfortunately, his journeys took a bit too long and his love sold herself into slavery to make money for her family. Now Bareris must track her down and hope that she's not been harmed by whoever owns her. Another storyline is that of Tsagoth, a blood fiend, in his geas to assassinate one of the zulkirs of Thay. A third story line follows Aoth Fezim, a rider of the elite Griffon Legion and wizard of some power, and his Griffon, Brightwing, in their battles with the invading horde of undead.

Still more story lines are woven in, including Dmitra Flass, Malark Springhill, priests of Kossuth, Red Wizards, zulkirs, Szass Tam and a host of undead. And, speaking of undead, why are the Red Wizards hiding their operation/experimentation in the realm of necromancy?