Captain Underpants and the Big, Bad Battle of the Bionic Booger Boy - Part 1: The Night of the Nasty Nostril Nuggets is the first of a two-part story of Captain Underpants book series. Both books count as the sixth and seventh novels in the titles.
After being humiliated by George and Harold, Melvin Sneedly tries to use his Combine-O-Tron 2000 to
combine himself with a robot. But when Melvin sneezes while the machine is counting down, it combines three elements instead of two like Melvin wanted: The Robot, Melvin, and his mucus, causing him to turn into a bionic booger boy who is evil.
On demonstration speech day in Ms. Ribble's fourth grade English class, George Beard and Harold Hutchinsshow off a new prank of theirs, the Squishy. The idea is to place fold two ketchup packets in half and carefully place them under a toilet seat so the next person who sits on the toilets gets ketchup sprayed all over the back of their legs (or the front, if they push down the toilet seat while standing in front of it). They demonstrate by putting two ketchup packets under the lid of a large garbage can with a toilet seat taped to the top. George and Harold each grasp one side of the toilet seat and together push down, making the class thrilled (except for the two kids sitting directly in front of the toilet seat, who were sprayed with ketchup.)
All the fourth graders (including Ms. Ribble, who had become quite different since the last book) want to try it out, so they leave to the cafeteria to get some ketchup packs, but Melvin Sneedly, the bossy nerd from Book 2, forces blocks the classroom door and forces everyone to get back to their seats and watch his show and tell project since there are only 15 minutes left before lunch. He then shows off to the class a combining machine called the Combine-o-Tron 2000. Using his hamster, Sulu, and a robotic hamster body he built, Melvin uses his invention to combine the two elements so Sulu is now a bionic hamster and waves a metal detector around Sulu with the reading going off the chart. Melvin then wants to demonstrate his new powers to the class.
Since Sulu has special powers, Sulu no longer obeys Melvin. When Sulu does not respond to any of Melvin's commands, he later threatens to hit Sulu with a paddle if he doesn't demonstrates any of his new powers. Sulu unexpectedly grabs both the paddle and Melvin and then spanks Melvin continuously. Melvin starts wailing and blubbering though Sulu hadn't really spanked him, and calls him a "bad hamster" and tells Sulu that he never wants to see him again for as long as he lives. Melvin then runs out of the classroom crying and everyone, including their Ms. Ribble, run behind chanting "Squishies!") George and Harold stay behind to confront the forgotten hamster and assure him not to feel bad, as Melvin is a real meanie, and Harold asks him if he wants to come home with them and live up in their tree house. Sulu jumps onto George and Harold's shoulders and licks their faces. George officially adopts the bionic hamster and Harold tucks him into his shirt pocket. The three friends head off to the lunchroom.
Meanwhile, the school principal, Mr. Krupp, comes marching into the office in a particularly foul mood. He stops beside Miss Anthrope's desk, huffing and puffing, and asks for his coffee. Miss Anthrope responds "Get it yourself, tubby!" and Mr. Krupp tells her he doesn't need her lip today and demands his coffee right now. Edith instead asks for him to get her a cup, too, while he's at it. Mr. Krupp screams in frustration and grabs a newspaper, heading toward the faculty restroom. After getting pranked with a Squishy by Ms. Ribble, he storms out of the door and vows to get George and Harold, but Ms. Ribble laughs that she actually did it, and introduces the Squishy as the latest fad. Mr. Krupp, however, doesn't believe her, and searches for the two in the cafeteria. On the way he notices many other victims in the hallway that have fallen to the Squishy (mostly first, second, third, fifth, and sixth graders) complaining about ketchup stains on their lower clothing. Mr. Krupp then yells at George and Harold that he got ketchup in his underpants as well as half of the kids in the school. George and Harold protest they never did any of those pranks despite demonstrating it and some of the fourth graders support them. Unfortunately, Melvin does not agree with any of them and proudly tattles they taught the prank to the other fourth graders during demonstration speech day. Mr. Krupp then thanks him for the proof and points George and Harold to the detention room as punishment.
George and Harold are angry that Melvin is a big tattletale, so they decide to teach him a lesson and get even as well. During last period, Melvin becomes furious when George and Harold make a Captain Underpants comic book starring him as an evil mayor who creates a robotic jail who jails people for unusually minor refractions. Finally, when Melvin becomes the victim of a Squishy, he decides to get his revenge on the boys.
Melvin goes home and builds a robot that is larger than him and has various powerful abilities. His idea is to combine himself with the robot so he will have special powers like Sulu, that way he can get revenge on George and Harold and astound the female students, Ms. Ribble and Mr. Krupp. Unfortunately, Melvin sneezes at the last moment (this was due to him sneezing a few times due to being allergic to the family cat Danderellla), so he gets combined with the robot and boogers, turning him into the Bionic Booger Boy.
The next day, George and Harold have Sulu do a trick during show and tell day by using watermelon seeds to destroy a dead tree. The kids are so amazed that they start cheering and petting Sulu. Soon Melvin comes in as a disgusting bionic booger monster to the shock and disgust of his classmates and Ms. Ribble. He explains that he tried to combine himself with a robot the night before, but sneezed at the last second causing his boogers to combine with him too. Melvin explains he is already trying to build a Separatron 1000 to reverse the process, but it will take 6 months to finish due to the complexities of cellular separation. George suggests switching the Combine-O-Tron's batteries around to reverse the process, but Melvin calls that the dumbest idea he has ever heard of.
Melvin is very disgusting now, but not unhappy because there are some positive sides to being a bionic booger boy. He's now the star football player (no one wants to tackle him because he's covered in boogers) and ace volleyball server (no one wanted to hit it back due to the ball being covered in mucus). He even gets his own personal drinking fountain since nobody wants to use it after he globbered all over it. While most of the kids are jealous of this, George and Harold aren't as considering the many villains they faced previously, they are just glad Melvin hasn't become a villain who would want to destroy the world.
Cold and flu season comes, however, and Melvin begins to act differently, he starts sneezing a lot and when Ms. Ribble asks him to not forget to cover his mouth, it only made things worse due to the gooey mucus being spread everywhere when Melvin covers his mouth when he sneezed again. Ms. Ribble then says "On second thought Melvin, don't cover your mouth next time."
The next day, Ms Ribble for some reason is out sick with a cold. Mr. Krupp is put as a substitute, but is shocked to find almost everyone wearing raincoats and umbrellas. He demands an explanation for this before Melvin sneezes. Mr. Krupp returns a few moments later with fresh clothes, a raincoat and an umbrella. When Mr. Krupp tells them they are going on a field trip to Snoddy Bros. Tissue Factory, Melvin starts speaking like Frankenstein and declares out "Me no like tissues!", shocking all of the other students.
When the class visits the tissue factory, they take a tour though Melvin is the only one that is terrified. After the tour, Mr. Snoddy offers to give everyone tissue packs. Melvin refuses (he calls the tissues "bad magic"), but Mr. Snoddy assures him that everyone loves them and that these tissues can really help wiping out mucus. He then throws a couple onto Melvin, but this causes Melvin to become gigantic and evil as a natural defense against the tissues (as well as the Flexogromnic-steel in Melvin's endoskeleton). Melvin's growth and angers destroys the bulding and the various things surrounding the building and he kidnaps Miss Anthrope before storming out to the city..
George and Harold get Mr. Krupp to turn into Captain Underpants to save the day. He saves his secretary, Edith Anthrope, from the Bionic Booger Boy, and she gives him some wet kisses as thanks. The water from the kisses unfortunately turns him back into Mr. Krupp and he gets caught by the Bionic Booger Boy when he demands an explanation from George and Harold, on why he is in his underwear. George and Harold try to get him to become Captain Underpants again through finger snapping, but due to Mr. Krupp's face still being covered by the slobbery kisses the snaps have no effect. Melvin swallows Mr. Krupp whole and then he goes for George and Harold.
Before Melvin can eat George and Harold, Sulu comes in to save the day and defeats Melvin. First Sulu hits Melvin on the head with a big cane. Then hits him in the belly with a big boxing glove. Finally, Sulu gets a pair of big teeth and snaps Melvin in the tushy. He then falls unconscious onto the ground with news people telling the story right next to his unconscious body. Melvin's parents, who are scientists, come in and pledge to try to help turn their son back to normal. By George's suggestion, they reverse the batteries in the Combine-o-Tron 2000 though it was only to prove to George that it will not work. The process somehow surprisingly works, and Melvin and Mr. Krupp are brought back, with the robotic booger globs flying off and landing on three building walls. They are unfortunately combined together for some reason, so Mr. Sneedly fires another blast and they are seemingly back to normal.
However, Mr. Krupp and Melvin start acting strange, with Mr. Krupp claiming credit for building the Combin-o-tron 2000, and saying, "You guys are so immature!" and Melvin giving punishments to George and Harold and claiming will punish them so badly that their kids will be born with detentions. The robotic booger globs then come to life and one of them then destroys the Combine-o-Tron 2000, causing Melvin's parents to flee for their lives. The three Robo-Boogers then chase Melvin, Mr. Krupp, George, Harold, and Sulu with George saying "Oh no!" and Harold saying "Here we go again!".