To Kill a Warlock by H.P. Mallory

The murder of a dark arts warlock.
A shape-shifting, ravenous creature on the loose.
A devilishly handsome stranger sent to investigate.
Sometimes working law enforcement for the Netherworld is a real bitch.
Dulcie O’Neil is a fairy. And not the type to frolic in gardens. She’s a Regulator—a law-enforcement agent who monitors the creatures of the Netherworld to keep them from wreaking havoc in the mortal world.
When a warlock is murdered and Dulcie was the last person to see him alive, she must uncover the truth before she’s either deported back to the Netherworld, or she becomes the next victim.
Enter Knight Vander, a sinfully attractive investigator sent from the Netherworld to work the case with Dulcie.
Between battling her attraction to her self-appointed partner, keeping a sadomasochistic demon in check, and fending off the advances of a sexy and powerful vampire, Dulcie’s got her hands full.
As the body count increases, Dulcie finds herself battling dark magic, reconnoitering in S&M clubs and suffering the greatest of all betrayals. From Goodreads

This wasn't as good as I had hoped but it was okay for a free book. It is full of paranormal creatures which I like and I hadn't guessed the "bad" guy. I have another free book lined up from this author and I might read that and then decide if I want to buy any of her books.

This book qualifies for:
Goodreads 2013 Reading Challenge
Serious Readers 2013
Tower Teams Read 2013-2
2013 Ebook Challenge
NBRC Stuck in a Rut
2013 Paranormal Reading Challenge (witch)
2013 Witches & Witchcraft Reading Challenge
2013 Why Buy the Cow? Reading Challenge (free on Amazon.com 24th of May 2013)