Mystery Walk, published in 1983, was Robert R. McCammon's fifth novel, and his first to be published in hardback.
It's the story of the first 21 or so years in the life of Billy Creekmore, who has inherited his mother's ability to see ghosts and ease the troubles of the ones who have not yet managed to pass on from the earthly realm into the more peaceful places that wait beyond. The novel opens with Billy's mother (she's very pregnant with him), progresses on to his first childhood experiences of the supernatural, and eventually turns into a coming-of-age story that involves his going out into the world to try to figure out the purpose of his "mystery walk" through life.
This was the novel that turned me into a McCammon fan. I'd forgotten that until rereading it, but it's true; I'd thought it was Boy's Life that had turned that trick, but that was a failure of memory on my part. No, it was this one; and not for the reasons you might think.