Sacrificial Magic (Downside Ghosts #4) by Stacia Kane

READING, WRITING, AND RAISING THE DEAD

When Chess Putnam is ordered by an infamous crime boss -- who also happens to be her drug dealer -- to use her powers as a witch to solve a grisly murder involving dark magic, she knows she must rise to the challenge. Adding to the intensity: Chase's boyfriend, Terrible, doesn't trust her, and Lex, the son of a rival crime lord, is trying to reignite the sparks between him and Chess.
   Plus there's the little matter of Chess's real job as a ghost hunter for the Church of Real Truth, investigating reports of a haunting at a school in the heart of Downside. Someone seems to be taking a crash course in summoning the dead -- and if Chess doesn't watch her back, she may soon be joining their ranks.
   As Chess is drawn into a shadowy world of twisted secrets and dark violence, it soon becomes clear that she's not going to emerge from its depths without making the ultimate sacrifice.