This is book one in The Devil's Dances Trilogy of Jubert.
I didn't know quite well what to think about this novel, it was pretty weird. In the book the main character is Roberta who works for the ministry of defense and is also a witch. She partners up with a fresh out of the academy cop to go to the historical city of London and find a killer. These historical cities are tourist spots that made out to be famous cities from certain time periods. London is set in the late 19th century . The whole time I wondered what was the actual time period of the book but there was no reference to what year it was.
What they find is that Roberta and Clement (rookie cop) have stumbled on a diabolical plot to summon the root of all evil, Satan himself. Now Roberta and Clement must travel to different historical places and stop this evil plan from unfolding. The book has a fantasy feel for it but it soesn't run the whole novel. Its a good thriller novel.