Captain Underpants: Book 13

The thirteenth installment in the Captain Underpants series (Captain Underpants and the Devilishly Diabolical Deeds of Doom) is a continuation of the 2015 novel Captain Underpants and the Sensational Saga of Sir Stinks-A-Lot.

Synopsis
George and Harold continue to voyage across time and space in search of their pets Crackers and Sulu. Little do they know that every time they travel through time, they rip the fabric of space-time more and more. Eventually, Captain Blunderpants, the evil clone of Captain Underpants from the eighth Captain Underpants book, is brought back! George and Harold begin to get bored, and zap themselves back to the present, only to see a distorted version of Earth completely conquered by Captain Blunderpants. They decide that only one person can save them now---Captain Underpants! But Mr Krupp is no longer able to turn into Captain Underpants due to Sir Stinks-a-Lot taking away his power, so the two boys zap back to the first book of the series to order a second 3D Hypno-Ring. They also decide to take their past selves with them after they hypnotize Mr. Krupp and defeat Dr. Diaper, unaware of the consequences. After that, they attempt to zap back (or forward) to the third book, where they steal some Super Power Juice, along with their other past selves. After they do this, they return to the present (again,) where they are apprehended by an even worse version of Earth, now not only conquered by Captain Blunderpants, but overrun by Talking Toilets and Giant Evil Zombie Nerds, due to Captain Underpants not being there to fight the Talking Toilets in Book 2 and Zorx, Klax, and Jennifer in Book 3. The three Georges and three Harolds run to their house, where they find Yesterday George and Yesterday Harold. Now, the four Georges and four Harolds run to Mr. Krupp's now destroyed house, where they have to use his household objects to fight off a Talking Toilet who ate Mr. Krupp. Once they do that, they recover Mr. Krupp, hypnotize him, and feed him the Super Power Juice. Captain Underpants is back!

So, the four Georges and Harolds venture with Captain Underpants to find Captain Blunderpants. Captain Underpants momentarily battles his evil self, but he is ultimately crushed and eaten by a zombie nerd. Helpless, the original George and Harold decide to zap back to exactly before that moment. Captain Blunderpants and Captain Underpants fight once again, but this time, Captain Underpants is victorious. Captain Blunderpants decides to find a way to eradicate Captain Underpants so he can go back to absolute power. He apprehends his assistant, Melvin Sneedly. He explains that simply pouring water on him can restore him to just a helpless, grumpy principal. He then proceeds to shoot water from his upgraded Robo-Squid suit. George and Harold retaliate by shooting water back. They then realize the Robo-Squid can be used for far more than time travel. They begin to shoot heat-seeking missiles at Melvin's Super-Soldier-Squid suit. He is temporarily downed. George and Harold are boosted up by their past selves and flung upward to Captain Blunderpants. They latch on to his leg, and snap their fingers. Captain Blunderpants turns into Nice Mr. Krupp, and George and Harold use the Robo-Squid Suit to send him and the other three Georges and Harolds back to where they belong.

Because of the timeline being altered, everything around them begins to change back to normal. However, George and Harold forgot they still need to find Crackers and Sulu. Suddenly, a vortex pops out of nowhere, and out comes two familiar-looking friends, who happen to be Crackers and Sulu, but this time they have changed; with increased intelligence and the ability to speak, they explain to George and Harold that after they caused the Big Bang, the explosion sent them to a distant part of the galaxy where they encountered a strange element called Lexonite, which evolved them and made them smarter. They show the two a couple red Lexonite Crystals, offering to “share their knowledge of the known universe” with George and Harold. The boys accept their offer, but suddenly a giant green hand swipes the Lexonite crystals from Crackers’ and Sulu’s hands. The culprit is revealed to be a giant, spoiled, greedy, birthday-obsessed girl who wants the Lexonite crystals as her birthday present. Crackers and Sulu tell the girl that the Lexonite is not to be messed with, but the giant girl just walks away destroying several buildings in her path of destruction.

George, Harold, Crackers and Sulu chase after the giant girl, with George and Harold once again saying “Oh, no!“ and “Here we go again!”

Trivia

 * The book was originally being worked on under the working titles Captain Underpants and the Deathly Destruction of the Dastardly Doppleganger and Captain Underpants and the Devilishly Diabolical Deeds of The Inter-Dimensional Doppleganger of Doom
 * The ending ties in with the next book in the series, Captain Underpants and the Ballad of the Brutal Birthday Girl Brawl, which is a crossover with the PBS Kids series WordGirl.
 * The word "diabolical" is intentionally misspelt on the cover of the book as one of Captain Blunderpants' dirty tricks.