The monstrous Turbo Toilet 2000 is determined to take revenge on George, Harold, and Captain Underpants.

The truth, the whole truth, and nothing but the truth about Captain Underpants -- George and Harold -- Don't you hate it when a kickball hits Uranus? -- Melvin's moment of mirth -- He-who-must-not-be-flushed -- Big Melvin returns -- Sanitized for your protection -- The incredibly graphic violence chapter, part 1 (in Flip-O-Rama) -- Everybody loves Melvin -- With great power comes a great big pain in the hiney -- It's a mad, mad, mad, mad Melvin -- Dark foreshadows -- Headin' home -- Eleven minutes later -- What was to come next -- To thine own self be truant -- Super-secret test day -- The idea -- Our doppel gäng -- The pact -- Shift workers -- Problems -- Super Diaper Baby 2 1/2 -- Dream a little dream of us -- Twin pranks -- Twelve days of chaos -- Heeeeeeeeere's Johnny! -- Disguise crazy! -- One smashed into the cuckoo's nest -- The incredibly graphic violence chapter, part 2 (in Flip-O-Rama) -- Tears of a commode -- The re-retaliation -- Surprise, surprise, surprise! -- To make a long story short -- Welcome back, Krupp -- Hamsterdactyls -- All's well that ends poorly.