George and Harold have been ordered to stop making comic books about Captain Underpants. So the boys put their creativity to work and invent an all-new superhero instead. Super Diaper Baby is faster than a speeding stroller, more powerful than diaper rash, and able to leap tall buildings without getting a wedgie! Now, Deputy Dangerous wants to steal Super Diaper Baby's powers and take over the planet. Will the diaper-wearing dynamo defeat the deputy, or is the entire Earth doomed?.