Captain Underpants and the Invasion of the Incredibly Naughty Cafeteria Ladies from Outer Space
Dav Pilkey
 Zorx, Klax and Jennifer, three evil aliens, land on the school roof and plan to take over the Earth by finding a way into the school turning the students and staff into giant monsters. Meanwhile, George and Harold learn in science class about the effects of mixing baking soda and vinegar together (into a paper mache volcano). After messing with the teacher, they decide to play a prank on the cafeteria ladies by giving them a fake recipe that involves mixing baking soda and vinegar. The recipe is disguised as a cupcake recipe with instructions to make a set of "Mr. Krupp's Krispy Krupcakes" for Mr. Krupp's birthday. The lunch ladies decide to surprise Mr. Krupp and make cupcakes for the entire school. As a result, they make a batch 100 times the intended size, and the school is flooded with green goop. Furious, the lunch ladies go to Mr. Krupp's office and instantly blame George and Harold for the incident ("But it wasn't even my birthday!"). Mr. Krupp explains that although he knows very well that the duo was responsible, he needs proof to punish them. Furious from past harassment by the two boys, the lunch ladies quit. Soon after, Zorx, Klax and Jennifer, come into Mr. Krupp's office very badly disguised as humans and apply for the vacant cafeteria job. Not suspecting anything, Mr. Krupp hires the three. As punishment for their antics, despite the fact that he still doesn't have any proof and that they did not mean for such a large batch to be mixed, Mr. Krupp takes away George and Harold's cafeteria food privileges and forces them to eat their lunch in Mr. Krupp's office from then on. The next day, the aliens, disguised as the lunch ladies, give "Zombie Nerd Milkshakes" for lunch, so everyone in the school except for George, Harold, and Mr. Krupp becomes a zombie nerd. After sneaking out of Mr. Krupp's office, George and Harold immediately notice what has happened to almost everyone in the school. Sneaking into the lunchroom, George and Harold learn that the aliens plan to feed the zombie nerds growth juice, turning them into giant minions bent on taking over the world. George and Harold steal the carton of growth juice and pour the contents out the window, most of which on a dandelion. After convincing Mr. Krupp that something is wrong, the three go confront the lunch ladies. The boys are able prove to Mr. Krupp that the lunch ladies are aliens, but one of the aliens snaps his tentacle (noted by George as a physical impossibility) at them, turning Mr. Krupp into Captain Underpants and prompting him to run away and fight crime. The boys temporarily defeat the aliens and by that time Captain Underpants has returned. They are unable to defeat the zombie nerds, so the three escape to the school roof and into the alien spaceship. Inside they steal Anti-Evil Zombie Nerd Juice, Ultra Nasty Self-Destruct Juice, and Extra-Strength Super Power Juice. before Zorx, Klax and Jennifer lock them in a cell. While the three aliens gloat, George and Harold switch the labels of the evil growth juice with the Ultra-Nasty Self Destruct Juice and the signs of the Spray Gun with the Fuel Tank, tricking the aliens into making the spaceship self-destruct rather than putting Rapid Growth Juice in the Spray Gun. Captain Underpants jumps off the spaceship with George and Harold before it explodes, claiming that he can use toilet paper to swing to safety. Of course, the toilet paper cannot support their weight and they instead use Captain Underpants cape as a parachute. They end up landing near a mutated dandelion which the boys accidentally created with the growth juice earlier, which begins to eat Captain Underpants. George reluctantly gives some of the "Extra-Stength Super Power Juice" to Captain Underpants, who kills the dandelion with his new powers. Harold mixes the Anti-Evil Zombie Nerd Juice with rootbeer, and transform all the zombie nerds back to normal, as well as turn Captain Underpants back into Mr. Krupp. However, as a result of the Super Power Juice, Captain Underpants permanently has super powers and the book ends with George and Harold hanging onto Captain Underpants's cape as he flies out the window.