Kevin's book is a mysterious book containing writing that he doesn't understand
The book has black covers with clearly aged papers, and it contains writing not known to mankind (Kevin at least)
A mysterious man brought the book to the cave where Kevin was knocked out after he took it from a box titled "Hillbilly Origins". Kevin found the book in the cave immediately after he woke up. He unsuccessfully tried to read it after leaving the cave.
The book looked different when it fist appeared in the prequel episode Hillbilly Origins.