Captain Underpants and the Tyrannical Retaliation of the Turbo Toilet 2000, is an upcoming book in the Captain Underpants series. It was announced to be released on August 26th, 2014.
The story begins where the last book left off with Melvin kidnapping George , Harold, and Captain Underpants. He takes them to the present where Tippy Tinkletrousers is pursuing their past selves to the past. George and Harold question why Melvin saved them because in the past, Melvin had hated them. Melvin simply replies that 'he had his reasons'.
Meanwhile, the kickball that one of Wedgie Woman's robots kicked into outer space was heading towards Uranus and decapitates the Incredible Robo-Plunger and the juice that came from the Robo Plunger poured into the Turbo Toilet's mouth. The Turbo Toilet comes back to life and decides to take vengeance on Earth. He took apart the Robo Plunger, made a rocket scooter and flew from Uranus to Earth.
On Earth, the police were searching for George, Harold and Mr. Krupp for 'they' robbed a bank in Book 8. However the police gave up and Melvin was very happy due to the absence of George and Harold. Two weeks later though, the Turbo Toilet 2000 invaded and annoyed Melvin, who needed just one/two hours to complete his project. He insulted the Turbo Toilet 2000, who gave chase. Melvin retreated to Jerome Horwitz Elementary School where he cowered in Mr. Krupp's office. He notices a toenail from Mr. Krupp, and he tosses it away in disgust. However, he remembers that Mr. Krupp is Captain Underpants and he could extract his DNA to him. Melvin started searching for the toenail again. Eventually the Turbo Toilet 2000 finds him, but Melvin finds the toenail, converts it to a juice, and drank it. Melvin then gained superpowers and destroyed the Turbo Toilet 2000.
Later on, Melvin becomes a super hero. One year later, he has had enough for the citizens were abusing the system, for requests such as help for dropping their wallet in the toilet. Melvin tracks down Captain Underpants, George and Harold using a tracking device he placed on Sulu. The story comes back to the part where Melvin has took the heroes back to the present. Melvin warns them of 'something that would happen in two weeks' and teleports to the unknown. When they get home, George and Harold needed a lot of sleep due to the fact they had not slept for the past thirty hours. However, their angry parents punish them by making them do chores. Unfortunately for them, they had to stay up all night studying for a test. The next day, they sleep in during the test, causing the boys to be separated due to the fact George would pass but Harold failed.