Ben Aaronovitch's bestselling Rivers of London urban fantasy series - "The perfect blend of CSI and Harry Potter." --io9

A mutilated body in Crawley. A killer on the loose. The prime suspect is one Robert Weil, possibly an associate of the twisted wizard known as the Faceless Man. Or maybe just a garden-variety serial killer.
Before apprentice wizard and Police Constable Peter Grant can even get his head 'round the case, two more are dropped in his lap: a town planner has gone under a tube train, and there's a stolen grimoire for Grant to track down.
So...

Ben Aaronovitch's bestselling Rivers of London urban fantasy series - -The perfect blend of CSI and Harry Potter.- --io9 - 2015 Locus Recommended Reading for Fantasy
When two young girls go missing in rural Herefordshire, police constable and wizard-in-training Peter Grant is sent out of London to check that nothing supernatural is involved.
It's purely routine--Nightingale, Peter's superior, thinks he'll be done in less than a day. But Peter's never been one to walk away from someone in trouble, so when nothing overtly magical turns up he...

Ben Aaronovitch's bestselling Rivers of London urban fantasy series - "The perfect blend of CSI and Harry Potter." --io9
Suspicious deaths are not usually the concern of Police Constable Peter Grant or the Folly--London's police department for supernatural cases--even when they happen at an exclusive party in one of the flats of the most expensive apartment blocks in London. But the daughter of Lady Ty, influential goddess of the Tyburn river, was there, and Peter owes Lady Ty a favor.
Plunged into the alien world of the super-rich, where the basements are bigger than...