Unique setting and characters.
Any book that starts out "The librarian and her mule spotted it at the same time" makes me want to read on. I'm not sure what the slippery "pannier" the author then talks about is--maybe it's the mule's, maybe it's the librarians, but I can look that up. And I've heard ages ago about the "blue-skinned people of Kentucky," so I can look that up to refresh my memory. Very different!