This one went a little further into the sci-fi/fantasy realm for my usual taste but it seemed to work.
Our hero, John Taylor, is a detective, in the noir sense of the word, who "finds lost things". He was born and raised in a hidden, darker side of London, Nightside, where horror and fantasy are the reality. He takes a case to find a runaway that was mysteriously drawn into Nightside by some unseen and previously unknown force.
The story reminded me of a heavier version of Mike Carey's Felix Castor series. Whereas, Castor operates in the realm of reality with the physical limitations of such, Taylor's world does not know these boundaries.