Captain Underpants and the Terrifying Return of Tippy Tinkletrousers, the ninth book in Dav Pilkey's bestselling series, sees the return of the villainous Tippy Tinkletrousers. The story opens with Principal Krupp in prison, where he witnesses Tippy's escape in a giant Robo-Suit. Tippy then sets his sights on George and Harold, who are wrongly imprisoned in juvie. Just as they're settling in, the time-traveling tyrant pulls them from prison.