Captain Underpants and the Attack of the Talking Toilets

JH Elementary School is planning on hosting its second annual Invention Convention. Upon seeing the poster for it, George and Harold think to themselves what it would be like to be principals for the day, but Mr. Krupp bans George and Harold from the convention this year and puts them in study hall all day because last year’s Invention Convention had to be called off as a result of them putting glue in everyone’s seats except their own. While getting ready to secretly sabotage everyone's inventions after thinking it isn't fair, the two boys run into Melvin Sneedly, who is busy working on his invention, the PATSY 2000, a photocopier that can make a simple two-dimensional image come alive. He demonstrates by putting in a photo of a mouse; out comes a real one, going on the floor. George and Harold assume Melvin put the real mouse in earlier, but they promise not to sabotage it, as long as he doesn't report them and eventually promises. Because of George and Harold's pranks, the convention has to be called off again, and Melvin breaks George and Harold's promise and tattles on them after Mr. Krupp is left confused as he knows that he had thought he put George and Harold in study hall.

An infuriated Mr. Krupp throws them in detention for the rest of the school year, threatening them with suspension if they leave the classroom once for any reason. George and Harold get assigned writing lines for two hours after school. With each boy using a quick line-writing device, they write all their lines in three-and-a-half minutes, then they pass the time by making a new Captain Underpants comic: Captain Underpants and the attack of the Talking Toilets. They decide to go to the copy machine, but realize that Mr. Krupp will suspend them if they leave the room and they decide to sneak out without Mr. Krupp catching them. However, the copy machine is surrounded by most of the teachers, so they copy off of Melvin's machine as they still believe it is a normal copy machine, but the talking toilets come to life as George and Harold discover that Melvin was right all along as they make a run for it. While fleeing, George and Harold are eventually caught red-handed by Mr. Krupp who was walking in the hallway and are suspended. The boys try to explain what happened in the gym, but Mr. Krupp refuses to listen and doesn't care since George and Harold are suspended and orders them to leave the school, much to George and Harold's dismay. All the teachers celebrate in the gym with Ms. Anthrope notifying George and Harold's parents to tell them the news and Ms. Ribble destroying George and Harold's desks, but the trouble begins when Mr. Meaner, the gym teacher, is promptly eaten by one of the toilets. Ms. Ribble then snaps her fingers at a toilet, making Mr. Krupp turn into Captain Underpants. George and Harold chase him as he takes several pairs of underwear from unsuspecting clothes lines.

Back at school, the trio finds only Ms. Ribble on the toilet table. The trio slings chipped beef with his underwear, and the toilets vomit all the teachers out and die. Soon after, the Turbo Toilet 2000 bursts out of the school and despite Captain Underpants's efforts, he swallows Captain Underpants whole. The boys sneak into Melvin's machine to make a super-powered robot called the Incredible Robo-Plunger 2000,{ but they first think of a giant robo yarran calld the yurrinator] which plunges its plunger into the Turbo Toilet 2000's mouth, letting the boys save Mr. Krupp. He fears that he will be fired for the damages, but the Robo-Plunger repairs all of it, and flies off to Uranus with the command never to return. In return, Mr. Krupp cancels their detention and as the principals, the boys hold an all-day carnival for the students and put the teachers (and Melvin for his tattling) in detention. At the end of the day, Mr. Krupp questions how the carnival will be paid for; and the boys reveal they sold his antique furniture and some more items. Mr. Krupp gets furious, and Miss Anthrope snaps her fingers after the boys, making Mr. Krupp become Captain Underpants again.

Early versions of the book say "Another Epic Novel by Dav Pilkey" instead of "The Second Epic Novel by Dav Pilkey".

Characters who appear in this book are:

• George Beard: One of the students at Jerome Horwitz Elementary School. He is friends with Harold Hutchins.
• Harold Hutchins: In the same school as his friend, George Beard.
• Mr. Krupp: Jerome Horwitz Elementary School's grumpy principal who despises George and Harold.
• Captain Underpants: A superhero from George and Harold's comics, George and Harold accidentally hypnotize Mr. Krupp into thinking he's Captain Underpants.
• Melvin Sneedly: The school genius, tattletale and George and Harold’s nemesis.
• The Incredible Robo-Plunger: A robot who beats up the Turbo Toilet 2000. He is made by the PATSY 2000.
• Madison Mancini: A student who invented the Automatic Dog-Washer that was ruined by George and Harold.
• Donny Shoemyer: He invented the Electric Ping-Pong Ball Server which was also ruined by the pranking duo.
• Freddie Moore: A student who invented the Volcano Detector.
• Ms. Ribble: The teacher of Jerome Horwitz Elementary School.
• Miss Anthrope: The school secretary.
• Mr. Meaner: The gym teacher at Jerome Horwitz Elementary School.
• The Talking Toilets and the Turbo Toilet 2000: The villains of the book. The Turbo Toilet 2000 returns on his own in the eleventh book, Captain Underpants and the Tyrannical Retaliation of the Turbo Toilet 2000.

• The Adventures of Captain Underpants, the first Captain Underpants novel that Dav Pilkey made in 1997.
• Captain Underpants and the Invasion of the Incredibly Naughty Cafeteria Ladies from Outer Space, the book that follows this one.
• Children's literature
• Dav Pilkey
• Captain Underpants, the series Dav Pilkey made.
• Captain Underpants and the Tyrannical Retaliation of the Turbo Toilet 2000