Scholar of Decay by Tanya Huff

A tale of fear from best-selling author Tanya Huff
"Scholar of Decay" is the story of a man driven by love into the darkest corners of the world. When Aurek Nuiken's wife is attacked and made prisoner by an evil mage, he must search the Domains of Dread for the spell that will allow him to free her. But ultimately his wife's freedom - and his own - lies in the hands of a clan of wererats who are not inclined to assist him. Faced with both his own torment and the monsters of the Ravenloft world, Aurek is pushed to the edge of madness and to a choice that no man should ever have to make.