Hammer of Witches — Niall Teasdale

Ceri Brent and Lily Carpenter, a sorceress and a half-succubus, are new to police work after becoming Special Advisors to the Greycoats, but when Ceri and her werewolf mate, Michael, find a charred corpse she finds herself frozen out of the investigation. As the bodies pile up they begin to investigate anyway, especially when their friends are threatened by the Witch Hunter's widening list of criminals to be tried, convicted, and burned alive.

But the Witch Hunter appears to have divine help and Ceri's faith will be tested to the limit before he can be finally brought to justice. What can a girl who stopped going to church at the age of seven have faith in when the country is invaded by angels?