A Certain Slant of Light by Laura Whitcomb
This book for me was a much better ghost story than Restless: A Ghost's Story (see previous post). It is the story of Helen and James two ghosts, or Lights, who possess two teenagers bodies and fall in love. This is not only a ghost story or a romance, it is also a mystery. It is a mystery because Helen and James do not remember how they died or why they didn't move on to Heaven.
Besides the story of Helen and James, it is the story of Billy and Jenny, their host bodies. Billy is a drug addict who has left his body. Jenny's overly strict religious parents have forced her spirit to flee its body. I won't tell you what happens with these two couples because that would spoil the mystery of it all.