When Mark celebrates his one-year anniversary on Earth, he decides to go return to Yugopotamia and he marries Princess Mandie and becomes king while his father, King Gripullon, disguises himself as Timmy and goes to Earth. Mandie takes over Yugopotamia with an iron fist, but even that isn't enough. She wants another planet as well: Earth.
Timmy and his fairies join Mark in his spaceship in the Dimmsdale junkyard to celebrate his one year anniversary on Earth. To commemorate this special day, Mark plays a video showing his escape from the evil and insane princess Mandie. It also shows him in his new disguise as Justin Jake Ashton, whom his true love Vicky adores. Just as Mark declares he's never leaving Earth, his ship is pulled off the planet by a Yugopotamian royal retrieval ship. Back at Yugopotamia, Timmy and Mark are brought before the latter's parents: King Gripullon and Queen Jipjorrulac. Grippulon reveals that the reason for this sudden capture was because someone is trying to eliminate him, as evidenced by the many mysterious lasers that are constantly being shot at him. He now wants Mark to become King of Yugopotamia so he can go into hiding.
Timmy takes the stand by vowing to find out who was behind all this while Grippulon hides on Earth, posing as Timmy using his fake-i-fier. He briefly informs Grippulon about his mannerisms and that the answer for every question is "I didn't do it." Soon after his father leaves and his mother goes on vacation to Spa Planet, Mark Chang is quickly crowned king. Just as Timmy gets his detective gear on, Mandie storms into the palace halls, revealing herself as the would-be assassin who was planning on making King Gripullon paranoid and go into hiding so that Mark would become king so she could forcibly marry him. She also anticipated that Timmy and his fairies would also be with him and thus, she shrinks the latter, diminishing their magic. After Mandie's robot army completely surrounds Mark, preparing to shoot him with a bazooka if he refused to marry her, Mark decides to give in and wed Princess Mandie. Shockingly, it is then revealed that Mandie didn't truly love Mark but really had a desire to take over as the ruler of Yugopotamia. The princess then gets her robots to lock Timmy and Mark in the highest tower while Mandie planned on destroying Earth. Mark becomes frantic, scared of missing his date with Vicky; also, it was seemingly impossible to defeat Mandie since she is the greatest warrior in the universe. However, after Mark shows the "love markings", or rather scars that he got from Vicky for looking at other girls or being late, Timmy realizes something and corrects Mark: there is another warrior in the universe even tougher than Man-DIE.
Using Mark's elastic tentacles, Timmy and Mark escape from the tower (reminiscent of Rapunzel and her hair, only Rapunzel was never yanked down the tower via her hair) and they flee Yugopotamia after scooping up the tiny figures of Cosmo, Wanda, and Poof. Once again, Princess Mandie takes chase and follows them, only to quickly get shot down by Mark's spaceship.
Timmy and Mark then arrive on Earth, meeting up with Grippulon in the process. Timmy then has Mark delay meeting up with Vicky. When she arrives, ticked off that he was late, Mandie touches down, seeing through Mark's Justin Jake Ashton disguise. Mandie demands that Mark be hers, but in an instant, Vicky easily beats her up, repetitively slamming her body on the floor. Timmy then takes Mandie's shrink ray to restore his shrunken god family back to normal. Mark then rejoices in a romantic moment with Vicky, only for the emotions to short out his fake-i-fier, causing her to reject his alien form and simply walk away.
Finally, with Mandie exposed and Grippulon no longer in danger, the Yugopotamians take the former back to their planet to imprison her and end her marriage with Mark, allowing him to stay on Earth until he feels he's ready to become King of Yugopotamia. Meanwhile, back at home for Timmy, he soon learns that Grippulon had made a few mistakes in his life: his parents believed that his gaining a deep voice and eating garbage was a sign of puberty. Therefore, they begin giving him only garbage for food and his dad locks him up in a cage made of wood, fearing a wild mood swing. Elsewhere, Cosmo magically shrinks his family down again so that their voices will sound high-pitched and squeaky again, making for an entertaining show.