Showing Agents of Light and Darkness by Simon R. Green

John Taylor, private detective with a difference, is back in the Nightside - that nightmarish realm hidden deep beneath London where it is forever 3 a.m.

This time he must use his supernatural gifts to locate The Unholy Grail - the cup from which Judas drank at the Last Supper - before it falls into the wrong hands. All who touch the cup will be corrupted - but they will also gain tremendous power.

So it's no surprise that Taylor isn't alone: angels, demons, sinners and saints are all determined to find The Unholy Grail, no matter what the cost. And it isn't long before they realize exactly who can lead them to it...