Captain Underpants and the Big, Bad Battle of the Bionic Booger Boy - Part 2: The Revenge of the Ridiculous Robo-Boogers is the second of a two-part story of Captain Underpants book series. Both books count as the sixth and seventh novels in the titles.
The three Robo-Boogers, Carl, Trixie and Frankenbooger, chase our heroes through town until they are cornered in an alley. They are about to destroy the four heroes when Sulu swallows them and then spits them into outer space. As everyone prepares to go home, it becomes obvious that there was a mistake with the Combine-o-Tron 2000, and now Melvin and Mr. Krupp have switched bodies. Several jokes are made with this outline, including "Kruppy the Kid" (Mr. Krupp in Melvin's body) roars and Ms. Anthrope to give him coffee or he would fire her. Seeing only a fourth grader, Ms. Anthrope gives him a wedgie. As for "Mr. Melvin" (Melvin in Mr. Krupp's body), he is also the basis of some abuse as he runs to hug his mother, who only sees a guy in his underwear coming to give her a hug, and promptly and ruthlessly assaults him with her purse.
After these incidents, George and Harold discover the mix up and explain it to Mr. Melvin and Kruppy the Kid. Mr. Melvin notes he could solve this problem right away if he still had his Combine-O-Tron 2000, but the Robo-Boogers smashed it in the last book. Understanding they'll need to use that invention to get everything back to normal, Kruppy the Kid orders Mr. Melvin to build a new Combine-O-Tron, but Mr. Melvin says that will take six months. Kruppy yells at Mr. Melvin he has got a school to run. Mr. Melvin apologizes and says building a cellular combiner is extremely difficult. It is not easy like building something like a robot, a time machine, or a PATSY. George suggests making a time machine to get the Combine-o-Tron back. Struck with what was originally George's idea, Mr. Melvin snaps his fingers. But oddly, Kruppy the Kid becomes Captain Underpants, his alter ego and the superpowers somehow following Mr. Krupp into Melvin.
When "Kruppy the Kid" (in Melvin's body) turns into Captain Underpants, George and Harold are forced to tell the secret of Captain Underpants to "Mr. Melvin", who was utterly fooled by this because Captain Underpants is bald and Mr. Krupp has hair (it's strange that the kid with perfect grades couldn't see through Mr. Krupp's bad toupee). They guess that the reconfigured Combine-O-Tron must have somehow transferred the super powers to Melvin's body when it blasted Mr. Krupp and Melvin a second time. Mr. Melvin, after finding out, declares to George and Harold once he gets his Combine-O-Tron back and reconfigure it, he is going to keep the superpowers in his body to make himself a superhero. He then threatens George and Harold to make a comic about him defeating Captain Underpants and becoming the world's best superhero (he also tells them to give him a cool name and to not make him look stupid), or else he will make the teachers give them 12 extra hours of homework for the rest of their lives.
Since it would take a long time to make a new Combine-O-Tron, Mr. Melvin decides to build a time machine, which is built in one day. He builds it in the school library, which is run by Miss Singerbrains, a biblioclast (book hater) (this is a response to the banning all of the books). The idea is that no one goes to the library because it only has one book in it. After getting a purple potty from the basement, Mr. Melvin tells Ms. Singerbrains she is fired for the rest of her life.
Later after finishing the time machine and getting George and Harold into the library, Mr. Melvin explains to George and Harold that they must be careful with the time machine, because if it's used two days in a row (the machine needs to cool off every other day it's used), some unknown bad thing will happen (an oppozo dimensional reality rift will open up if this occurred). He tells them to use the Forget-chama-call-it 2000 on anyone that sees them on their journey, so that way nothing bad will happen to the delicate timeline and change the future. George and Harold go back in time two days and retrieve the Combine-o-Tron after it gets Melvin and Mr. Krupp back to normal, but before it is smashed (they replace it with a look-alike). This is done thanks to the use of the Forget-chama-call-it on Melvin's parents.
They go back to the time machine in the library, where Miss Singerbrains steals the Combine-o-tron and the Forget-chama-call-it and drives off to the police station. The boys go back in time and get a Quetzalcoatlus ("Crackers"), then go back to the moment when Miss Singerbrains stole their stuff, then get their machines back thanks to Crackers. Miss Singerbrains is convinced she is dreaming because pterosaurs don't exist at this time. Harold goes to return Crackers back to his/her own time, then they erase Miss Singerbrains's memory and go back to their own time.
Meanwhile, Kruppy the Kid, as Captain Underpants, has been getting into trouble by doing stuff like preventing the school football team from winning an important game by stealing the ball, which he mistakes for a UFO (the opposing team then tackled him which caused the home team to lose). Kruppy the Kid also destroys the skateboards of three skateboaders since they refused to go away from a no skateboarding area. He then spanked them as punishment for everyone. Kruppy the Kid then tries to rescue a cat from a tree. This backfires as Kruppy the Kid leaves two ladies he was trying to help across the street in the tree. The football team, the skaters, and the old ladies are now mad at Kruppy the Kid. Mr. Melvin gets Captain Underpants to come to them. He uses the Combine-o-Tron to switch them, so Melvin and Mr. Krupp are back in their own bodies, but Melvin sneakily gives himself Captain Underpants's superpowers.
Meanwhile, in space, Carl, Trixie, and Frankenbooger grab onto a spaceship that was examining Uranus, where the robot and the toilets from Book 2 are. They hang onto the spaceship as the spaceship goes back to Earth. Once on Earth, they start destroying the spaceship center.
Captain Underpants, despite the fact that he doesn't have super-powers, decides to go after the robo-boogers. George and Harold follow him. They originally lose to the robo-boogers, but figure out that the robo-boogers die when they come into contact with oranges (the vitamin C in the oranges counteracts against the cold that made the boogers evil). This way, they beat Carl, but Trixie & Frankenbooger become more cautious and dodge the oranges.
Captain Underpants defeats the Robo-Boogers by standing on top of John's House of Toilets (the top of the store is a giant toilet lid) and doing an annoying dance. The Robo-Boogers start to climb up the building, when they get hit by a well-placed Squishy.
Soon George and Harold have to answer questions for the Eyewitness News crew, but Melvin comes and lies to the Eyewitness News crew, saying he beat the Robo-Boogers with his super-powers. While Melvin tries to make Captain Underpants bow down to him, George and Harold sneak back to the school. George and Harold then return with the Combine-o-Tron 2000 & Forgetchamacallit-2000. They then use the Combine-O-Tron on Melvin and Captain Underpants, giving Captain Underpants his super powers again. They then erase the memories of the news crew and the TV audience with the Forgetchamacallit-2000.
Melvin wails about how he's not a superhero anymore, but everyone doesn't care because he was a selfish jerk for the past two books. George states to Melvin he should just be happy he didn't get his comeuppance, however Melvin does get his comeuppance when the people Mr. Krupp and Captain Underpants bugged while they were in Melvin's body (Miss Anthrope, the football team, 2 old ladies, and 3 skateboarders) come back for revenge on him. They then chase him down into the sunset. As George and Harold leave back to their treehouse, they use a water fountain to splash water on Captain Underpants' face and return him to his Kruppy old self.
When George and Harold return to their clubhouse, George learns that Harold did not take Crackers back to the dinosaur age, but is keeping him/her as a pet, like Sulu. Harold asks if they can keep him tonight. George agrees, but they take him/her back tomorrow.
The next day, George, Harold, Sulu and Crackers go into the time machine to send Crackers back home, even though Melvin said something about not using the time machine two days in a row. Harold is hesitant on using it, but George assures Harold that nothing bad will happen if they use it two days in a row. The book ends with them starting the time machine, and something bad happening & with George yelling "OH NO!" and Harold yelling "HERE WE GO AGAIN!"
- On pages 21-23, when George, Harold, Mr. Krupp, and Sulu were cornered by the Robo-Boogers, next to them were a garbage can and two boxes. On pages 21-22, the box on the ground has a flap on its side. But on page 23, the flap disappears. Also, the garbage can has a handle that changes from side to three-quarter view.
- The people in the space shuttle see robots and toilets on Uranus. This is a reference to Captain Underpants and the Attack of the Talking Toilets where the Incredible Robo Plunger took all the evidence regarding the talking toilets to Uranus and was told to remain there.
- However this is an error because In the 4th book the space shuttle discovered them as seen in the newspaper Professor Poopypants was reading. Then again, It could have been a different space shuttle.
- After Mr. Melvin snapped his fingers, you can see Kruppy the Kid's underwear is ripped. This happened while Harold was pulling Kruppy off the coat hanger while George cut his undies with some hedge clippers.
- When the space explorers were running out of the space shuttle, one of them was wearing boxers and bunny slippers.
- Crackers is too small to be a Quetzalcoatlus (as she is about as tall as Harold, when in real life, the Quetzalcoatlus was as big as a World War II Spitfire).
- This is the only Epic Novel where the narrator does not say "But before I can tell you that story, I have to tell you this story." at the end of Chapter 1.
- This book is also the only book where at the opening page it doesn't show George, Harold, and Captain Underpants running away from the villain(s) and Captain Underpants doesn't seem to be aware of the situation. In this book it shows George, Harold, Mr. Krupp, Melvin, and Sulu running away from the three Robo-Boogers which is where the last book left off.
- The Everything Except Fabric-Softener Store makes its second appearance in the series. Its first appearance was in the fifth book.
- This is the only epic novel that does not feature incredibly graphic violence in a flip-o-rama.
- This is also the only epic novel that does not feature Mr. Krupp's regular ego in his own body.
- Captain Underpants official site
- [ Dav Pilkey official site