Vengeance (Demons of the Nothing #1)

Christopher Kelsey has spent a lifetime working in the police department, but his free time is consumed by work, leaving him with little time for the fun things in life. His friends say he needs a partner or a dog. He doesn't want either.
His latest case is the most bizarre he's ever come across. Black magic, demons and more, all he wants to do is dig through the delusions to find the truth.
Is the stunning apparition that only he can see real? Or is it a sign he should have quit years ago? The more Christopher investigates, the stranger the case becomes. Can he solve it and retain his sanity? Or will the invisible stranger extract a price he's unable to pay?