Blood debt - Tanya Huff

It began with a ghost in his bedroom. A tormented soul hungry for vengeance. The sort of nocturnal visitation that even a five-hundred-year-old vampire like Henry Fitzroy found tiresome. It would lead Vicki Nelson, PI into her most deadly investigation yet.

The wraith is determined that Henry and Vicki track down its killer - and is prepared to use a little persuasion by way of the innocent inhabitants of Toronto to ensure their support. Forced to investigate, Vicki discovers a host of souls in desperate torment and evidence to suggest that trailing the killer will only lead to further deaths - starting with her own.