George and Harold are "C" students (and bad spellers), but they are very good at "saving the entire planet from the nasty forces of unrelenting evil" and also at ketchup-toilet pranks. Unfortunately, they can't save Melvin Sneedly from getting paddled by his bionic hamster. But, frankly, they wouldn't want to, because besides being the school brainiac, Melvin is also a tattletale. When his robot-making hobby backfires horribly, Melvin transforms himself into the Bionic Booger Boy instead of a bionic superboy. Can Captain Underpants save everyone from this "greenish, glistening behemoth?"