Devil's Business — Caitlin Kittredge

Pete Caldecott did everything she could to save Jack from Hell, even reigning in the dark machinations of the Morrigan to help bring him home. Still, Black London has not welcomed Jack back with open arms. . . So when a friend in Los Angeles asks for help tracking a sorcerous serial killer, Pete and Jack decide a change of scenery couldn't hurt. . .

But the shadow side of the City of Angels turns out to be more treacherous than they ever imagined. Together, Pete and Jack must navigate a landscape teeming with hostile magic-users -- and fight an unknown enemy. When their investigation leads to a confrontation with the demon Belial, Jack learns that he wasn't the only thing to escape from Hell. Now it's up to him and Pete to track and eliminate an evil older than the Black itself -- before it turns L.A. into Hell on Earth. And destroys life as they know it back at home...