Bloodbath (Harrietta Lee Book 2)

Harrietta Lee has a friend who can see the future, and she's just gone missing.
She's not the only one. There are too many disappearances to count, and Harry can't be everywhere at once--which is why she's enlisting the help of a fumbling, fedora-clad detective, a programmer who moonlights as a DJ, and your friendly neighborhood demon, Lilith.
Well, "help" is a relative term...