Just Another Judgement Day. Nightside Book 9

Judgement Day has arrived for the inhabitants of the Nightside, and here to cast the first stone is God's very own agent of righteousness, the Walking Man. The Walking Man, God's enforcer on earth, has arrived, and brought Judgement Day with him. His sole mission is to rid the Nightside of sin and corruption - trouble is, that's exactly what the city was built on. It's a place where depravity rules, and where every dark desire can be fulfilled.
If the Walking Man is allowed to carry out his indiscriminate purge, there'll soon be nothing - and no one - left. So the Authorities have hired private eye John Taylor to stop him, although that's likely to be easier said than done. Everyone knows that the Walking Man can't be killed, but if John Taylor doesn't find his weakness soon, he - along with the entire Nightside - will be facing God's wrath.
Just another Judgement Day is the ninth title in Simon R. Green's New York Times bestselling Nightside series