Loose Change by A.R. McNevin

There’s very little special about Oliver Vance. He’s a middle man. He does what two/thirds of the people on the face of the planet does, while being hated by the other third for doing it. He brokers. He facilitates. The only difference between him and the billions of other middling people who middle their way through their lives; he plies his trade in a hidden world of veiled London.
One night, one of the more powerful gangland bosses of veiled London summons Olly to his club with a job; find his granddaughter and keep her safe. How hard could that be?
Accepting the job, Olly Vance, and the mysterious mystic Marie Beckett, would spend the next three days dodging vampires and eldritch horrors, negotiating with magic users of all stripes, all the while trying to keep the second coming of a race of mutants alive long enough to take her throne.