Set after the previous episodes "Spaced Out" and "Totally Spaced Out", Mark comes to Earth and tells Timmy that his planet, Yugopotamia, has been invaded by a cute alien race known as the Gigglepies. Since the Yugopotamians are afraid of anything nice and sweet, they're powerless against them. Timmy departs to fight the menace, but upon their arrival, Cosmo and Wanda fall under their spell. Can Timmy stop them himself?
The scene begins on Yugopotamia. The King and Queen call Mark for breakfast, and they all sit down and enjoy a box of "Invader O's" cereal. When they look inside, the three aliens hear something giggling, then all three of them start screaming in terror. Similar problems unfold for other Yugopotamians all over the planet as they open up their Invader O's cereal boxes. The planet is in chaos, but Mark manages to escape the planet and vows to enlist the help of the universe's mightiest warrior, Timmy Turner. Mark crashes his space ship into Timmy's bed room who screams in panic and has Cosmo and Wanda poof him into a Crash Nebula uniform. Timmy aims a giant laser a Mark, whom pleads Timmy that he is not there to cause harm and needs Timmy's help defeating "The Gigglepies", a race of cute aliens that appear as a "special surprise inside" offer on the Invader O's cereal boxes. Timmy is reluctant to leave at first, but quickly agrees when his parents call him and tell him Vicky is staying over to babysit. Mark Chang sends Timmy off in a separate spaceship, and promises to be right behind him, but stays behind anyways when he hears Vicky's voice.
Timmy and his fairies arrive on Yugopotamia and see that the place is now colorful and full of rainbows and sunshine, which is very unlike the Yugopotamians who hate beautiful things. Timmy runs into Trilly, one of the Gigglepies, and learns that they have taken over the planet. Timmy is not distracted by its cuteness and demands it take it to their leader. Back on Earth, Vicky is forcing Mark to do chores, but he loves the work she has given him. Vicky gives him a bag of manure to spread around the lawn, which Mark considers a delicacy and starts to eat it out of the bag. On Yugopotamia, Cosmo and Wanda have become obsessed with the Gigglepies, collecting them like toys and asking each other to trade the ones they have. Timmy is being tickled by two Gigglepies, but cries out to Cosmo and Wanda to not get distracted. On Earth, Mark has painted Timmy's house in good time, giving Vicky an idea. She convinces Mark that making money for her is a good way for an outsider like him to earn the love of a girl, so she uses him to paint Mr. Dinkleberg's house for him for an elevated price.
Timmy, Cosmo, and Wanda are being carried to the Gigglepie's castle. They go before Overlord Glee, the leader of the Gigglepies. Cosmo and Wanda have been hypnotized and are already bowing down to their new leader, but Timmy is unaffected. He sees the King and Queen, as well as the rest of the Yugopotamians, trapped in a prison cage nearby. The Overlord reveals that the Gigglepies invade planets by selling themselves and their merchandise, sucking the planet dry as their sales go up and the freedoms go down. The Gigglepies were only able to conquer the Yugopotamians because they fear them, but were not affected by their cuteness. Overlord Glee then suddenly changes to a demonic form stating "Isn't that cute?" before going back to normal. Timmy notes that is horrible and it didn't rhyme. Overlord Glee realizes that Timmy is onto them so he orders the Gigglepies to get him. Timmy frees the King, Queen, and other Yugopotamians, although he learns they were in the cage for their own protection and are too horrified to fight the Gigglepies. They gather around Timmy and start tickling him to death, through his laughter he cries out to Cosmo and Wanda to help, they turn to him for a moment but a Gigglepie tries to distract them again, however its rhyming was off so it doesn't keep Timmy's godparents completely hypnotized. Wanda snaps out of it and realizes Timmy is in trouble, and Cosmo tries to eat one of the Gigglepies but spits it out, saying that it tastes like manure. When the Yugopotamians hear this, the King tells Timmy that manure is the finest delicacy on their planet.
Timmy wishes that the Yugopotamians had forks, knives, bibs, and an empty stomach. They feast is on, and the entire army of Gigglepies are eaten by the Yugopotamians. The King and Queen thank Timmy and give him a "medal", King Gripullon coughs up a heart piece from a Gigglepie he ate which lands on Timmy's chest, who says "gross!" which they take as a compliment. Back on Earth, Timmy returns to Mark who does not want to leave because of his relationship with Vicky which has been taken to the next level, hard labor. But when Vicky comes in and hugs Mark because she is so happy he has made her so much money, he screams in agony and jumps out of the window, then flees in a spaceship back to his planet. At breakfast the next day, Timmy's parents award him for Mark's work with a box of Invader O's... Timmy and his parents check the surprise advertised inside the box, they hear a giggle which Timmy's parents think is cute, but Timmy starts to screams no!. The screen goes black with a shot of a Gigglepie laughing at the viewer. The gigglepies are in another episode.