George and Harold are up to their old tricks again and when their latest prank makes a direct hit on school Brainiac Melvin sneedly, he decides to get even. But in the blink of an eye and the sneeze of a nose Melvin goes from snooty to snotty and the bionic booger boy is born. Can Captain Underpants clean up this catastrophe or will the mucous monster make a mess of things.
