When George and Harold hypnotize their principal into thinking that he is the superhero Captain Underpants, he leads them to the lair of the nefarious Dr. Diaper, where they must defeat his evil robot henchmen.

"La última vez que vimos a nuestros héroes, Jorge y Berto, habían sido convertidos en zombis destinados a deambular por toda la eternidad en un planeta postapocalíptico. Pero, te preguntarás, ¿por qué razón el Capitán Calzoncillos no salvó a los chicos de ese cruel destino? Para empezar, ¡el profesor Cacapipí y sus alocados viajes en el tiempo impidieron que Jorge y Berto crearan al Capitán Calzoncillos! Ahora, habiendo cambiado el curso...

Principal Krupp once again turns into the superhero Captain Underpants in order to save the world, and Jerome Horwitz Elementary School, from the evil talking toilets and the Turbo Toilet 2000.

George and Harold have really done it this time--they've created a monster! She's faster, smarter, and more evil than anything the world has seen before--she's Wedgie Woman! With the help of her horrible robots and her horrendous hairdo, Wedgie Woman is on a mission to take over the world, and she'll give a whopping wedgie to anyone who stands in her way--including Captain Underpants.