A pink-haired girl named Stephanie moves to LazyTown with her uncle (the mayor of LazyTown), where she tries to teach its extremely lazy residents that physical activity is beneficial.
Stephanie, Mayor Meanswell's niece, arrives in LazyTown for the summer. She meets other kids—the game-addicted Pixel, the candy-loving Ziggy, the mischievous Trixie, and the spoiled Stingy—but notices something odd about them and the entire town. Nobody likes to play or have fun outside!
The kids are playing an astronauts game which inspires Robbie to move to the moon in order to get away from Sportacus and the noisy kids. Robbie flies to the moon closely followed by the kids who accidentally mistake him for an alien and back to Earth along with Robbie on board but they run into trouble and it is again up to Sportacus to save him.
Robbie decides to go back in time to stop Johnny SportsCandyseed from planting the SportsCandy trees. Sportacus and the kids need to stop Robbie before all the SportsCandy in LazyTown becomes missing forever.
When the kids play a Secret Friend game, a misunderstanding makes Trixie lose trust in Stephanie and leave town. With Sportacus away on an expedition, will they be able to save their friendship?
Pinocchio appears in LazyTown to help Robbie lie to the kids, convincing them to eat sugar gooey lollipops, Stephanie and Sportacus are in a race against time to bring them SportsCandy and help them regain their energy.
It's the final day of school and the kids are excited to finish the big last exam. But when Robbie needs to go to school to get himself proclaimed as the world's top villain, his cheating ways gets Stephanie into trouble.
Robbie discovers that to make LazyTown lazy again, he needs to get rid of Stephanie, who wants to be a real princess. So Robbie grants her wish and disallows her to leave her castle.
When the Mayor hears that Bobby Bird is coming to town, he tries to call him but instead Robbie gets the call and pretends to be him. He challenges Ziggy, who is terrible at basketball, to compete against him. But Ziggy practices and gets support from his friends and "Teddycus." But Robbie switches Ziggy's teddy bear with a mean Teddycus which hands him bad support.
When the Mayor and Stephanie go away Butterfly Watching and with Sportacus away to help them, Robbie Rotten disguises himself as a wizard and makes a potion to make the kids lazy.
The kids are having a sleepover and the mayor tells them a bedtime story about a baby troll. Ziggy decides he wants a pet troll so the kids venture into the mountains and find a troll named LuLu who begins to eat all of the sports equipment. Much to Robbie's delight, he disguises himself as a troll catcher as he thinks a bigger troll will eat more sports equipment but will the kids be able to return LuLu back home before she eats most of LazyTown?
Ziggy and Stingy put on a puppet show about a fortune teller which inspires Robbie to disguise himself as one to make the kids believe that there will be no Sportacus in the future. When Robbie hands Sportacus a sugar apple, it is up to the kids to rescue him.
During school, Trixie acts as a ghost and scares her classmates especially Ziggy. So Robbie decides to disguise himself as a ghost to scare the kids from the school. Meanwhile, the kids try to get rid of the ghost by squirting it with slime after a sports candy experiment mistake.
Stephanie and Stingy are playing spies. Robbie Rotten designs his own dream team, Bobby, Tobby, and Flobby Rotten who successfully capture Sportacus. Robbie then plans to blast him out of town with a cannon but his plan fails when he accidentally blasts himself out of town and it is up to the kids to save the day.
In the series finale, Robbie orders an Egyptian Pyramid with the hope of trapping Sportacus inside but the kids ruin his plans and Stingy makes things go crazy. Robbie disguises himself as a mummy but will Sportacus be able to save the kids?
