Crossbones - Diane L. Kowalyshyn

Keme didn't think his life could get worse until he's turned into a windigo--a creature with an insatiable appetite for human flesh. An attempt to end his life frees Arthur, the victim ensnared in Keme's internal soul-cache. Arthur is propelled into dominance and Keme recedes into obscurity. Two souls inhabit one body and the turnabout causes abominable evil to reign supreme.

Arthur exacts revenge on Nathanial, the man who ruined his mortal life, but eating him is too easy. Instead, Arthur systematically destroys everything Nathanial holds dear.

Arthur is captivated with Loretta, Nathanial's daughter, but Keme is in love. After a whirlwind marriage, Loretta realizes her husband is two diametrically opposed beings. Too late to save her father, she manages to outmanoeuver Arthur, and the coup triggers another soul switch. Now, she and Keme must launch a counterattack against Arthur's inhumanity, or go to hell trying.