Chapter 1: The Day the Lunch Lady Quit
* George and Harold, two fourth-graders, terrorize their teacher, Mr. Krupp, with a prank.
* The school's lunch lady, Mrs. Nathanson, witnesses the prank and resigns in protest.
* George and Harold accidentally start a fire in the kitchen, forcing the school to evacuate.
Chapter 2: Melvin's Mind-Control Ring
* Melvin Sneedly, a nerdy classmate, buys a mind-control ring from an infomercial.
* George and Harold discover the ring and convince Melvin to use it on Mr. Krupp.
* Mr. Krupp becomes a superhero named Captain Underpants, who fights crime and wears his underwear on the outside.
Chapter 3: Captain Underpants Strikes Again
* Captain Underpants defeats the evil Tippy Tinkletrousers, a giant talking toilet.
* George and Harold realize that Melvin has lost the mind-control ring and Mr. Krupp is no longer under their control.
* They create a new ring to regain control, but Melvin steals it and uses it to become the supervillain Professor Poopypants.
Chapter 4: The Curse of the Evil Lunch Lady
* Mrs. Nathanson returns to the school as the evil Lunch Lady, seeking revenge on George and Harold.
* She creates an army of zombie cafeteria workers and attacks the school.
* Captain Underpants and his trusty sidekick, Super Diaper Baby, fight the evil forces and restore order.
Chapter 5: The Revenge of Tippy Tinkletrousers
* Tippy Tinkletrousers returns for revenge, this time even more powerful.
* He creates a giant poop monster that threatens to destroy the school.
* Captain Underpants and his team, including Melvin as the redeemed Professor Poopypants, defeat the monster and save the day.
Chapter 6: The Invasion of the Robocalls
* George and Harold's prank calls using a fake phone number get out of hand.
* The phone company sends an army of robotic callers to track them down.
* Captain Underpants and his team battle the robots, transforming them into singing lawn chairs.
Chapter 7: The Unstoppable Toilet
* Melvin creates an unstoppable toilet that threatens to flush everything down the drain.
* Captain Underpants, Super Diaper Baby, and George and Harold team up to defeat the toilet.
* Melvin's mind-control powers fail, and he is sent to the principal's office for punishment.
