City of Masks by Daniel Hecht.
The main character is a ghost hunter, an empathic parapsychologist, who specializes in figuring out who the ghost is, what it wants and how to persuade it to leave.
This book was quite interesting in that unlike classic mysteries, you don't even find out the *crime* until well over halfway through the book, much less "who dun it". My husband and I listened to this as an audio book and kept guessing wrong all the way up until the final revelation! Very well done, I thought.
And the descriptions of the people and places are very thorough. I feel like I've really been to New Orleans now (before the flood). (Well, technically I have, but I was only 4 at the time and don't remember much!)
Anyway, I liked this and will be reading the sequel soon.