Ghost of a Chance — Dan Willis

When a bizarre string of locked-room murders terrorize New York, the police have no leads, no suspects, and only one place to turn. Now private detective Alex Lockerby will need every magical trick in his book to catch a killer who can walk through walls and leaves no trace. Unfortunately Alex's magic hasn't been working very well. He can't even manage to track down several truckloads of stolen goods, including one belonging to New York's preeminent sorcerer, Andrew Barton. To make matters worse, Alex and his clients are being stalked by a shadowy cabal with strange powers that Alex has never seen before. With the Ghost killer seemingly able to murder at will and the tabloids, the public, and Alex's clients demanding results, Alex will need a miracle to keep himself, his clients, and his reputation alive.