Tippy Tinkletrousers has traveled back in time again to undo the trouble he created by changing the past. Now, he has traveled forward in time and is chasing George and Harold to get his revenge on them. George and Harold decide to use their own time machine, the Purple Potty, to return their pet dinosaur to the past so Tippy Tinkletrousers won’t hurt it. By mistake Mr. Krupp, AKA, Captain Underpants is also transported back in time.  Back and forth, back and forth, back and forth through time they go. Harold and George see dinosaurs, meet cave people, and draw the first ‘comic book’ on the  cave wall to help them communicate with the cave people.  The cave people help George and Harold defeat the evil Tippy Tinkletrousers. While in the past Tippy is responsible for the Ice Age and the Big Bang Theory. Too bad Harold and George’s teacher doesn’t believe a word of this when they use their first hand information on their Science Test once they get back to the present.

Captain Underpants fans will enjoy this 10th epic novel with its two flip-o-ramas and George and Harold’s two comic books.

Librarians will enjoy the sturdy binding and heavier(than paperback’s) paper.