Helen, Martha, Skits, T.D., and Alice are lying on the Lorraines' lawn, when Truman runs up. He starts running laps around his friends and invites them to join in too, and reveals that he's become worried about his fitness levels since he was inactive as a baby and is weaker than Hercules. They all start running, except Martha, who takes a nap. Just before she falls asleep, Truman says that everyone must exercise, even heroes, but Martha thinks that heroes don't need to exercise as they're "perfect".
She then has a lucid dream where she, Helen, Truman, T.D., Alice, and Carolina have won a trophy for their work as the "Book Bots". After the intro (which Martha insists they do), Carolina reveals that the trophy was awarded after all the book-based criminals gave up, leaving the Book Bots out of a job.
However, Dr. O'Mayhem (portrayed by Ronald) is the only criminal who hasn't given up. He decides that he keeps getting caught because everyone's faster than him, so he must get in shape. However, finding that too hard, he decides to instead mess up exercise books to make people sluggish instead of fit.
He naps for a very long time, during which the Book Bots become sluggish, forgetful, and (in Martha's case) fat from inactivity. They decide that they need to get back into shape, so they take some books out from the library (while also discovering they've become physically weak).
They follow the instructions for a week, but it only makes it worse. Then, Helen realises that the title changed from Exercises to Increase Fitness to Exercises to Decrease Fitness, and they realise a crime took place and they're needed again. Carolina reveals that Dr. O'Mayhem has also changed yoga books so that they tie people into knots and then robbed the knotted people, and made it so that sailors can no longer tie knots.
When the Book Bots get to the harbour, they see that the rope has been tied into yoga poses instead of knots, so the yoga books and knot books must have been swapped. To solve the problem, the heroes use a knotted man to hold the rope in place, then they go to the library and use the Textinator to get all the books back to normal. They exercise to get themselves back to normal and go to confront Dr. O'Mayhem, who's been tied up by the knotted people.
Then, Martha wakes up to find her friends are a bit worn out. She fears her dream has come true, but they assure her that they just ran too much. Martha, however, is keen to run, and when she runs off, her friends perk up and chase her.
This episode provides examples of
- An Aesop: The episode has the moral of staying fit to avoid becoming fat and/or lethargic.
- Aesop Amnesia: This is one of those episode where Martha is still anti-cat following "There Goes the Neighbourhood".
- Alliterative Title: Fit Fights Fat.
- Animal Jingoism: Helen asks Martha if she wants to be strong enough to defend against cats.
- Blatant Lies: When the cat yowls at Martha, she yelps and jumps back, but then says, "I wasn't scared".
- But You Were There, and You, and You: Dr. O'Mayhem resembles Ronald Boxwood and his cat resembles Nelson.
- Call-Back: The Textinator from "Return of the Bookbots: the Case of the Missing Words" features again.
- Conforming OOC Moment: Even Alice gets tired from running.
- Crazy-Prepared: Truman thinks he must become as strong as Hercules just in case he needs to do the stuff Hercules did.
- Dark Is Evil: Dr. O'Mayhem wears all dark grey.
- Dream Episode: The most of this episode is a dream had by Martha.
- "Eureka!" Moment: When Dr. O'Mayhem wonders if he needs an exercise book to learn how to exercise, he then decides to change the exercise books to decrease fitness instead of increase it.
- Evil Laugh:
- Dr. O'Mayhem says, "Ha ha ha ha!" after planning to change the exercise books.
- He does another evil laugh when the Book Bots confront him.
- Fat Comic Relief: At one point, Martha causes a leak in the speedboat because she's so fat.
- The Fat Episode: While the human Book Bots remain the same size even after lack of exercise, Martha becomes so fat she's almost spherical.
- Fat Slob:
- When Martha becomes lazy from not doing enough, she becomes very round.
- Inverted for Dr. O'Mayhem, who's thin as a wire but also very lazy.
- Forgetful Jones: In addition to making them lazy, the lack of activity also makes the Book Bots forgetful — among other things, Truman can't keep track of his and Alice's checker game, Helen doesn't know what time it is, and Martha can't remember the definition of "lazy".
- From Bad to Worse: Due to Dr. O'Mayhem's tampering, the exercise book only makes the Book Bots even weaker.
- Heroic Dog: Subverted. Martha, along with the other Book Bots, tries to catch Dr. O'Mayhem, only to find that the knotted people already have.
- I Resemble That Remark!: Martha denies being "lazy" when T.D. says that everyone has become lazy, but then she says, "What's 'lazy'? I think I know but I don't feel like trying to think of it."
- I've Heard of That — What Is It?: Martha says, "I am not lazy — what's 'lazy'?".
- Kid Hero: Subverted. The Book Bots (the humans of which are nine-and-ten-year-olds) try to stop the criminal mastermind Dr. O'Mayhem, but the knotted people beat them to it.
- Lazy Bum:
- Dr. O'Mayhem decides exercise is too hard after just two push-ups and takes an extraordinarily long nap.
- Due to prolonged inactivity, the Book Bots also become lazy — Truman doesn't care whose turn it is in checkers
- Medium Awareness:
- Martha, in addition to being aware she's dreaming, is also aware of the "Book Bots show opening" and wonders why it didn't happen this time around.
- Everyone ducks to avoid the flying Book Bot logo.
- Morally Ambiguous Doctorate: The bad guy is Dr. O'Mayhem.
- Names to Run Away from Really Fast: The villain of the episode is called Dr. O'Mayhem.
- Offscreen Moment of Awesome: The knotted people tie Dr. O'Mayhem up and lock his cat in a cat cage offscreen.
- Opinion-Changing Dream: Before falling asleep, Martha thinks exercise is a waste of time, but when she wakes up, she wants to exercise.
- Pathetically Weak: After doing nothing for too long, Alice has trouble even carrying a book, then T.D. and Helen have trouble carrying it between them. Later, Truman can barely hold the Textinator.
- Punctuated! For! Emphasis!: Carolina reveals that the sailors' inability to tie knots is endangering baby ducks, and Helen says, "Not baby ducks!". Carolina says, "Yes. Baby. Ducks."
- Right-Hand Cat: Dr. O'Mayhem strokes a Nelson-esque cat.
- Rip Van Winkle: Dr. O'Mayhem takes a long enough nap for the Book Bots to become out of shape during it.
- Running Gag:
- Due to being lazy, the Book Bots keep groaning.
- Martha keeps mentioning her grudge against Dr. O'Mayhem's cat.
- Sleepyhead: Due to being very lazy, Dr. O'Mayhem takes a really long nap.
- Speak in Unison:
- After Carolina gives her friends the trophy, they chant in unison, "We beat crime! We beat crime!".
- The team yells, "Book bots!" in unison when they get their strength back.
- Superhero Episode: This episode focuses on Martha and the kids (except Milo, since he wasn't introduced when the show was created) working as "Book Bots" (literature-based superheroes) again.
- Temporary Bulk Change: Martha becomes very fat, but she returns to normal size when she and the others regain their strength.
- Tempting Fate: When it's said that the criminals gave up book crimes, it then cuts to Dr. O'Mayhem, who hasn't given up.
- Toilet Humour: Truman worries that he'll have to clean out a stable like Hercules.
- Training Montage: One scene shows a montage of the Book Bots training themselves to go back into shape so they can defeat Dr. O'Mayhem.
