Captain Underpants and the Invasion of the Incredibly Naughty Cafeteria Ladies from Outer Space (and the Subsequent Assault of the Equally Evil Lunchroom Zombie Nerds)

Captain Underpants and the Invasion of the Incredibly Naughty Cafeteria Ladies from Outer Space (and the Subsequent Assault of the Equally Evil Lunchroom Zombie Nerds) is the third book of the Captain Underpants series by Dav Pilkey. The series of American children's books are about two fourth graders, George and Harold, and their mean principal Mr. Krupp, who can turn into Captain Underpants. It was published on September 1, 1999. It is the first book to feature the use of 'Extra-Strength Super Power Juice' (an invention of Zorx, Klax, and Jennifer, the antagonists of the book), which is used to give Captain Underpants superpowers later in the book.

Plot
Zorx, Klax and Jennifer, three evil extraterrestrials, land on the roof of Jerome Horwitz. Meanwhile, George and Harold mess with their science teacher, then make the cafeteria ladies a fake recipe, disguised as "Mr. Krupp's Krispy Krupcakes" for Principal Krupp's birthday. The lunch ladies decide to surprise Krupp and make cupcakes for the entire school and the school is flooded with green goop. Furious, the lunch ladies blames George and Harold, but Krupp needs proof to punish them. Furious from past harassment by the two boys, the lunch ladies quit. Soon after, the aliens come in, very badly disguised as humans and Krupp hires the three. For the boys' antics, Krupp forces them to eat their lunch in his office. The next day, while Krupp has a banana, both boys have their own weird sandwiches and other junk food, causing a repulsed Krupp to exit his office.

After their lunch, the sign is already changed. They immediately notice that the school have become evil zombie nerds. 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 lands on a dandelion, turning it into the massive Dandelion of Doom. Krupp doesn't believe them, but starts to after Anthrope takes a bite out of his desk. When Harold escapes an alien's grasp, he pulls off her gloves in the process. The alien snaps her tentacle at them, turning Krupp into Underpants, who runs to the local shoe store for a cheeseburger.

The boys temporarily defeat the aliens by Underpants' return, but the three escape, soon into the alien spaceship, where they steal multiple cartoned juices, before the aliens lock them in their cell. While the aliens gloat, the boys switch the labels of the growth and self-destruct juices, along with the spray and fuel tanks. This trio jumps off the spaceship before it explodes and under Underpants' cape parachute, they end up landing near the Dandelion of Doom, which begins to eat Underpants. George reluctantly gives some of the "Extra-Strength Super Power Juice" to Captain Underpants, who kills the dandelion with his new powers. Harold mixes the Anti-Nerd Juice with root beer, which transforms the zombie nerds back. However, as a result of the Super Power Juice, Mr. Krupp (when Underpants) permanently has super powers.