The two begin taking turns making Mr. Krupp act in ridiculous ways, such as behaving like a chicken, a monkey, and then finally into the superhero from their own comics, Captain Underpants. However, Mr. Krupp jumps out the window to fight crime and the boys grab some supplies such as fake doggie doo doo. "Captain Underpants" eventually confronts two bank robbers at Frank's bank, who fall in hysterics. The police are about to arrest Captain Underpants too, before the boys whisk Captain Underpants away. Before they can change their principal back, the trio witnesses two robots stealing a large crystal and Captain Underpants' cape gets caught on their van, dragging him (and the boys) to an old, abandoned warehouse. There, the trio meet the evil Dr. Diaper, who plans to use the crystal to power his Laser-Matic 2000 to blow up the Moon, destroying every major city on Earth happens when Tippy Tinklertrousers changes what happens in book nine so that he can take over the planet. George and Harold escape and hide, but Captain Underpants is tied up.