"Vanish" by Tom Pawlik. About halfway through (in one sitting) and very intriguing. Couldn't put it down. Four Chicago area people from varying backgrounds wake up the morning after a weird storm and find that everyone else have vanished. There are strange other-worldly grey creatures hiding in the shadows watching them and (apparently) causing them to hallucinate. It's supposed to be a Christian novel, but I can't figure out how the author will resolve the box he's put his story into.