Captain Underpants and the Revolting Revenge of the Radioactive Robo-Boxersis the 10th book of the Captain Underpants saga. It was released by Scholastic Inc. on January 15, 2013.
The book picks off where the last one left off, where Tippy was crushed by the zombie nerd from Book 9. However, after an explanation on how elephants are slow due
to their heaviness even if they are shrunk, it is revealed that Tippy wasn't really squashed, because giant evil zombie nerds are incredibly slow. So, Tippy goes off to a convenience store and buys a cherry cough drop and a new bow-tie. Then, Tippy olives a extra-large ketchup packet and buys that too. Tippy saves himself with the ketchup packet.
He then travels four years ago and freezes Kipper, Bugg, Finkstein, and Loogie before his Tippy's Slightly Younger version arrives. When Slightly Younger Timmy does arrive, Future Tippy tells him that he is there to stop him from scaring the bullies. Then, he shrinks Slightly Younger Tippy and travels four years into the future. The bullies unfreeze and continue running as they were. Arriving in the present, Tippy sees that the timeline is back to normal, however he has also arrived at the point where Georgeand Harold were getting arrested in Book 8. He then freezes the cops, and chases George, Harold, Crackers, and Sulu around town. The next day, George and Harold are still hiding from Tippy's robotic freezing pants.
They then go to to to the school to save the two pets by traveling 65 million years ago and leaving them there. However, Mr. Krupp then gets mad that the two are running away from him while he is asking them to tell him why they are late to school. It then turns out that he is there with a box of curtains, because they keep on disappearing. When George and Harold reach the library, they lock the door behind them, so Mr. Krupp won't get in. However, Mr. Krupp begins to unlock the door with his keys. He then bangs on the Purple potty demanding that they come out. However, then, Tippy then appears again, and is about to freeze Mr. Krupp. However, when they go back in time, Mr. Krupp also goes with them. (As, he was standing too close to the Purple Potty.) Tippy then sends Tiny Tippy back in time when George and Harold were going in the Purple Potty. Tiny Tippy then learns that they're going to the Mesozoic era. He then tells his two selves the news, and the three Tippys go back 65 million years.
Meanwhile, 65 million years ago, George and Harold notice that Mr. Krupp is also there with them. Harold goes out to grab his hand, but then Tippy kicks the tree. The five are then knocked down and the Purple Potty is then destroyed. George, Harold, and Mr. Krupp are saved by Crackers and Sulu. However, Mr. Krupp does not know this yet. Then, Tippy threatens to kill George and Harold. So the boys snap their fingers at Mr. Krupp, turning him into Captain Underpants.
As Tippy chases the five, Tiny Tippy and Slightly Younger Tiny Tippy become tired of letting regular Tippy boss them around, so they go back in time to chapter 8 of book 9 to get the Goosy-Grow 4000 from the top half of their suit so that way they can grow bigger than big Tippy. Slightly Younger Tiny Tippy then zaps Tiny Tippy and turns him into Supa Mega Tippy. Then, Supa Mega Tippy betrays Slightly Younger Tiny Tippy, who climbs onto his suit as a stowaway. He then goes back 65 million years ago when Big Tippy captures Captain Underpants, who up until then thought that they were playing chase.
Big Tippy then falls into a lake, turning Captain Underpants back into Mr. Krupp. Just then, Supa Mega Tippy and Slightly Younger Tiny Tippy arrive. Tippy then tells the two that Captain Underpants' weakness is water. However then, Supa Mega Tippy then tells Big Tippy that HE is going to destroy Captain Underpants, not him. Out of anger, Big Tippy sets off his nuclear bomb. But Supa Mega Tippy kicks him into another part of the world. However, the bomb still blows up, killing the all the dinosaurs. The six then travel to a time about 200,000 years ago, when cavemen first existed.
Supa Mega Tippy then captures George, Harold, Crackers, and Sulu. Sulu then tears a hole through Tippy's robotic hands, and the four friends fly off, promising Mr. Krupp that they'll come back for him. Tippy then holds Mr. Krupp hostage under a waterfall until further notice.
Meanwhile, the four friends travel over to a cavepeople village, asking for help. However, they don't understand their accent. Tippy then attacks the village, forcing them all to seek refuge in a cave. George and Harold discover that the cavepeople understand pictures better, so they write a wordless comic book on the cavewalls to help the cavepeople that Tippy is evil and he must be stopped.
After the cavepeople finish reading the comic, they and the duo all start drawing out plans on how to stop Tippy. They then set up traps for Tippy and even burn up his robot pants. And when he fires the Freezy-Beam 4000 at the cavemen, Slightly Younger Tiny Tippy tampers with it so it won't turn off. Tippy tries his hardest to turn it off, but the emergency shut off is stuck. The ice spreads throughout the destroyed village quick, and into the mountains. Slightly Younger Tiny Tippy then steals the Goosy-Grow 4000, and zaps himself to a range of 120-150 feet. As he is about to reach 200 feet, the Goosy-Grow 4000 then falls on the ice, spreading it throughout the world.
George, Harold, Crackers, Sulu, and the cavemen run over to Mr. Krupp to free him. However, the ice encases over everyone and freezes them. When all hope seems lost, Tippy, now 200 feet tall, grabs everyone with his robotic hands. Then, George and Harold snap their fingers again, turning Mr. Krupp back into Captain Underpants. Captain Underpants rips off Tippy's robotic pants, leaving him standing there in his boxers.
Using the pants as a net, Captain Underpants, George, Harold, Crackers, and Sulu take to cave people over to France, giving them a new place to live. When they return to Tippy, asking for a ride back to the future, Tippy squirts water from the water bottle at Captain Underpants' face, turning him back into Mr. Krupp. While they are all falling, Crackers is getting sicker and sicker for some strange reason. Tippy then captures the five with his hand, and they all get ready to go back home. George and Harold both vow to start acting more mature and take their classes seriously as they go forward in time.
About 200,000 years later, the five notice that they're home. As they are celebrating, they notice that everything looks so old. Then Tippy tells them that he will not hurt them, but is going to destroy Captain Underpants, and that's why he brought them thirty years after the present, so that way the world doesn't have to get destroyed when Captain Unedrpants is destroyed. He then lets George and Harold go. Crackers is continuing to get sicker, so Sulu makes him a nest. The four friends watch as Tippy tosses Mr. Krupp around with his foot, laughing maniacally.
George and Harold however can't hear the battle due to the yelling teachers nearby. Suddenly, an old Mr. Krupp arrives and tells the teachers to get the students in class now. The duo discover that the screaming and yelling teachers are themselves in the future, but they're not very nice teachers and are actually teachers that are similar to the teachers they are used to. As it turns out, the vow that George and Harold made about promising to act more mature is what made them similar to the teachers they were used to.
In response, the duo make a new vow to always be themselves. After that, the adult George and Harold disappear, leaving old Mr. Krupp standing there confused. Then, they snap their fingers at him, turning him into Captain Underpants. The duo tell old Captain Underpants to save the present Captain Underpants. He does what he is told, and when he brings Mr. Krupp back down, George and Harold snap their fingers, making TWO Captain Underpantses. They each beat up Tippy and his giant robo-boxers, but Tippy then sets off his nuclear bomb. Tippy then states to the six that the bomb will destroy the entire galaxy, as it is more powerful then a supernova. Suddenly, Crackers and Sulu sacrifice themselves by sending themselves, Tippy and the Robo-Boxers back 13.7 billion years ago. When the three go back, the bomb explodes, causing the Big Ka-Blosh theory, incinerating Tippy and creating the universe.
13.7 billion years later, George, Harold, and Captain Underpants are stuck in the future without a time machine. Then, Harold points out that Crackers is a girl, because she laid three eggs. The three then decide to take care of the eggs, seeing as Crackers did something for them, so in return, they'll do something for HER. As the three are walking through town, Melvin appears in an octopus suit, and takes them to the present, telling them that something bad has happened since they've been gone