One day at Kastle Koopa, Larry had just found a Lucky Dime, but Roy stole it and ran off with it. Everyone soon found out, so they all tried to steal the coin while Bowser and his wife were away, but they soon came home, and they found out that Larry, Roy, Wendy, Lemmy, Iggy, Ludwig and Morton had made such a mess fighting for the Coin, the angry Bowser and Clawdia grounded them, then they remembered they´re going to the Koopa-Family Meeting the following day, and they were worried their kids would make such a mess like that time again, they called a Babysitter named Belle Evans Koopa.
The next day, Belle showed up early, and as all the kids introduce themselves, she gave them all Gold Medals, as Bowser and Clawdia left for their Meeting.
Later that day, Larry was playing Chess with Ludwig, but since he kept cheating, Ludwig got mad, and suddenly, Belle entered Larry's room, took away the Chess game and told both children : “No fun and games!”
Meanwhile, Lemmy and Iggy were practicing Karate to be as strong as their father, with Wendy as the referee, but then Belle arrived, worried about their fighting, and told them : “No fighting, otherwise the punishment will be bigger!”
A bit later, Morton was in the kitchen eating all the ice cream in the fridge, when Belle came in the kitchen and found him there! She got so angry, Belle got the whipped cream bottle in her hand and squirted it all over Morton! “You cannot enter the kitchen!” she demanded.
While that, Roy was practicing to shoot with his Bill Blaster when Belle came in his room and he shot her accidentally! Then Belle put his Bill Blaster in the locked cupboard so he couldn´t get it!
After lunch, everyone was trying to play a prank on Belle. They took a brick from the floor, fill it with slippery oil and put it back again! After that, Belle slipped over it and fell! She asked everyone who did it, but they answered "No". She knew that someone was lying.
At night, the children all chatted about how angry they were at Belle for not letting them have any fun. They tried to call their parents to tell them that Belle made up many unfair rules, but she didn´t let them use the phone. They all thought that it was like being in prison!
Everyone got fed up, but then, Roy has a plan! That night, Belle's dog, Beauty, was guarding the Koopalings at the door of their room, so, Iggy sneaked out and taunted Beauty, which caused her to get angry and chase him, giving Roy and Lemmy the chance to sneak out! Iggy then lead Beauty into the underground floor, where the Doomship was, so he commanded it to fire rapidly at her! Meanwhile, Belle tried to find Beauty when she heard the explosion of the Doomship.
But...suddenly...she saw Ludwig, Morton, Larry and Wendy sneaking out of the room, and she left to investigate, as Lemmy tried to stop Belle, but she got away with it!
A moment later, Wendy and Ludwig were spinning on the chandelier, making Belle angry after she spotted them, and Larry and Morton then let go of the chandelier, making it land right on Belle's tail! She screamed so high that she broke her crystal bow!
Then, Wendy taunts Belle, which made her to become free of the chandelier and chase Wendy all the way upstairs to the bedroom! Morton then taunted her some more, and escaped the area of the closet, right before Belle banged into it...and then, Larry opened up the closet, causing all of Wendy´s ugly-old-used-make up she forgot to throw out to land right on Belle!
Belle was REALLY MAD, as Morton kicked Belle at the same time as Lemmy and Larry took the elevator, and Iggy, Roy, and Ludwig were pushing the throne to hit Belle with the help of Wendy distracting her too!
Belle was REALLY STEAMED UP, as Roy , Morton, Ludwig and Iggy pull Belle down the stairs, and they knock out Belle! But the battle was not over yet! While still being knocked out, Lemmy freed the army from the dungeon, and they all blinded Belle by taking pictures of her with their cameras and flashes, and she then chased everyone all the way up to their bedroom...where an angry Beauty is roaring at them!
Finally, Roy goes for the final step of the plan! As everyone agrees with the plan, they chase Belle and Beauty through the maze, and the army of Goombas, Paragoombas, Paratroopas and Koopa Troopas got the slingshot ready, as it hit Belle and her dog, throwing them out of the castle! Everyone was then happy, when Bowser and Clawdia just arrived after their meeting.
And later that night, Roy, Iggy, Ludwig and Morton put the army away and Larry, Wendy and Lemmy told their story, Bowser and Clawdia understood that calling a Koopa babysitter is not the best choice, so they award their children with Gold Badges: Roy recieved the Team Leader Badge for leading the team and having the idea of the plan, Ludwig received the Best K.O. Ideas Badge for using modern ideas to defeat Belle, Wendy and Morton were awarded the Best Taunter Badges, for taunting Belle to get rid of her, Lemmy and Iggy are awarded the Best-Koopaling-Brothers Badges for being such good cooperating Koopaling brothers for helping save the day, and finally, Larry is rewarded the Best Helper Badge for helping on almost all traps, but they even had a Badge for their dad and mum! The Best Father Badge and the Best Mother Badge, for being the greatest father and mother they could ever have had!
Roy liked so much the defeat of Belle, after dinner he asked Iggy if he could make a game with all the details of the plan for him, Iggy and their brothers and sister.