George and Harold (the co-stars of the enormously popular Captain Underpants series) are in big trouble again! Their mean principal, Mr. Krupp, has had it with their comic books. But the boys aren't giving up, and they decide to create an all-new epic novel about a subject they've never tackled before!

Dr. Dilbert Dinkle started his career as an ordinary, everyday evil genius/inventor/bank robber. But when he awakens one day transformed into a walking, talking puddle of pee, he vows to destroy every toilet in town. Will the devious Dr. Dinkle and his conniving cat, Petey, ruin restrooms for the rest of us? Or could this be a job for the death-defying duo of Super Diaper Baby and Diaper Dog?