Hold onto your pants for this awesome adventure from the author of the million-selling Captain Underpants! Harold and George are back - presenting the sensational saga of two crazy kung-fu caveboys raising hell in 500,001 BC! Ook and Gluk have a pretty great life growing up together in Caveland, Ohio, even though they're always getting into trouble with their short-tempered tribal leader, Big Chief Goppernopper. But the boys' idyllic life takes a turn for the terrible when an evil corporation from the future invades their quiet town... With action, laughs, comic strips and flip-o-rama fun in every chapter, here's excitement aplenty to blow your pants off!