Captain Underpants and the Sensational Saga of Sir Stinks-A-Lot

Captain Underpants and the Sensational Saga of Sir Stinks-A-Lot is the twelfth and final book in the Captain Underpants series, written and illustrated by Dav Pilkey. The book continues after the eleventh book as George, Harold, and their clones switch places, only to find their gym teacher Mr. Meaner has become Sir Stinks-A-Lot, who turns his students into slaves. The boys team up with their adult counterparts to save the world.

Plot
On the planet called "Smart Earth", one scientist is mixing "smart" ingredients, but the planet explodes, one chunk landing at Piqua Valley Home. Gym teacher Meaner eats a chunk, and the other teachers follow him as he escapes. Yesterday George and Harold visits his office, where he sprays them with a strange substance which turns them into robot-like slaves. The other teachers are amazed at their behavior, though George and Harold are not, and they get sicker because of excessive homework. They see a commercial for the “Rid-O-Kid 2000” and disguise themselves as adults, making the children do silly things "for" the teachers. The teachers call in Mr. Meaner and enraged at what he sees, he gets out his Stinky Kong 2000, now a mech suit.

Deciding to seek help from adults they can trust, George and Harold go to their parents, only to find that they know they’ve changed and prefer it that way. Feeling heartbroken, they go to Melvin’s house to find his Robo-Squid, then travel forward in time to find their older selves, now famous graphic novel writers, and their families. The older and younger versions of George and Harold travel back in time to find Mr. Krupp. The older George and Harold tried to snap their fingers, but as he had been washing his face, he can not turn into Captain Underpants, and Mr. Meaner beats them up anyway. Once Mr. Krupp dries his face, they snap their fingers and turn him into Captain Underpants, defeating Mr. Meaner and sending him to prison.

After eating an egg salad sandwich with pickle relish, Meaner turns into a blob called Sir Stinks-A-Lot. Underpants returns to fight him back, but when Old George and Harold are captured and absorbed, Stinks-A-Lot discovers Captain Underpants' weakness and turns him into a powerless Krupp. Old George and Harold telepathically call for Sulu and Crackers' children, who feed him multiple items that makes him explode. As young George and Harold return their older counterparts, they find that Krupp doesn’t turn into Underpants at the snap of a finger. With covers over them, they travel back to find Crackers and Sulu, and the other ones wake to find even the children gone. Back at their tree house, Yesterday George decides that he and Harold make a comic featuring Dog Man.

Controversy
Captain Underpants and the Sensational Saga of Sir Stinks-A-Lot revealed the co-protagonist, Harold, to be gay. The plot of the novel shows the two protagonists, George and Harold, meeting future versions of themselves. Future George is married to a woman, and Harold is married to a man; each couple has two children. LGBTQ+ news reporter Steven Frank, from Logo News, commended the unostentatious nature of the book's gay representation, deeming the move a "big step forward for kid's lit." In October 2015, some elementary schools banned the book due depicting Harold as homosexual.

Adaptations
Elements of the novel were adapted to the second and third seasons of the animated series The Epic Tales of Captain Underpants.
 * Mr. Meaner's role as a super-smart villain would be loosely adapted in the second season episode "The Bombastic Blathering of Brainy Blabulous", where Mr. Meaner is turned into "Brainy Blabulous".
 * Harold's sexuality would be referenced in the third season episode "The Monstrous Mayhem of the Massive Melviathan", where Harold notes the "Moose-cle Men" who appear in the episode's shared dreamscape to have been from a "weird dream" of his.