Skin Trade (Anita Blake Vampire Hunter #17) by Laurell K. Hamilton

I'D WORKED MY SHARE OF SERIAL KILLER CASES, BUT NONE OF THE KILLERS HAD EVER MAILED ME A HUMAN HEAD. THAT WAS NEW.

My name is Anita Blake and my reputation has taken some hits. Not on the work front, where I have the highest kill count of all the legal vampire executioners in the country, but on the personal front. No one seems to trust a woman who sleeps with the monsters. Still, when a vampire serial killer sends me a head from Las Vegas, I know I have to warn Sin City's local authorities what they're dealing with.

Only it's worse than I thought: several police officers and an executioner have been slain paranormal style. When I get to Las Vegas, I'm joined by three other federal marshalls. Which is a good thing because I need all the backup I can get when hunting a killer this powerful and dangerous.