Let me just say this and get it out of the way: there is nothing in the supernatural realm occurring in this story, but there is a monster here. He is neither a vampire nor a ghost; he is not the dark forces of evil dressed up in a clown costume. He's just a person. And he got away with a horrendous crime.
While this isn't my favorite Stephen King novel, Mr. Mercedes is a good enough read for a lazy couple of days in that laying-on-the-beach kind of book-that-you-can-read quickly sort of way. It's a crime thriller with no supernatural elements involved, the perfect escape novel when you want something sort of mindless to read while you're relaxing in the summer sun. I've posted about this book over on the crime page of this reading journal.