For a Few Demons More - Kim Harrison

Despite dating one vampire and living with another, Rachel Morgan has always managed to stay just ahead of trouble . . . until now. A fiendish serial killer stalks the Hollows, and no one living in or around Cincinnati-human, inhuman, or undead-is safe.
An ancient artifact may be the key to stopping the murderer-a mysterious relic that is now in the hands of Rachel Morgan, fearless independent bounty hunter and reckless witch. But revealing it could ignite a battle to the death among the vast and varied local supernatural races.
Rachel's been lucky so far. But even she can't hide from catastrophe forever.