After Timmy, Chester and A.J. had finished watching an episode of Crash Nebula, they try to act it out. To make things more interesting, Timmy wishes for an alien. But he is brought a real one, the prince of a planet called Yugopotamia, named Mark. He captures Chester and A.J. (who don't know he's a real alien). Mark also falls in love with Vicky. Timmy must find Mark's parents so they can take him back to Yugopotamia before Chester and A.J. find out the truth!
Timmy, Chester, and A.J. were watching Crash Nebula in Timmy's bedroom. During the show, Crash Nebula attempts to save his comrades from aliens, but ends up as their prisoner as the episode ends. The cliff hanger excites Timmy and his friends, and after the show they pretend to fight each other: Timmy as Crash Nebula and Chester and A.J. as the two aliens. Timmy tipped over a nearby table and took cover behind it, while his friends shot at him with purple spray guns. Vicky overhears the commotion from downstairs in the living room, sniffs the air, and mutters "I smell fun". Timmy called Cosmo and Wanda, who are in outer space in their Mothership, the name of which puts Wanda in charge, much to Cosmo's chagrin. Timmy wished he had more firepower, and Cosmo grants the wish.
Timmy is magically poofed into a Crash Nebula costume. A gigantic cannon emerges from Timmy's arm guards, blasting a hole in Timmy's wall and narrowly missing his friends. Chester and A.J. are fascinated by Timmy's costume, and A.J. asks him where he got it. Timmy replies "Internet". Chester says that all they needed now was a real alien to reenact an episode of Crash Nebula. Chester and A.J. begin to leave, so Timmy quickly wishes for a real alien monster to play with. In a flash of light, a green squid-like alien named Mark appears in front of them. Timmy compliments his fairies on how lifelike it looks, to which they respond that they are not so good at creating aliens, so they borrowed a real one.
On the far off planet of Yugopotamia, King Gripullon asks his wife, Queen Jipjorrulac, what is troubling her. The Queen tells him that their son, Mark, had not tortured any prisoners today, to which the King agrees is very unlike him. The King's computer tells him that Mark had been taken to the planet Earth, which causes the King to quickly spring into action, vowing to destroy the "foul" planet at once, and then rescue Mark, to which the Queen glares at him to correct the order of which he does those acts. Back on Earth, Chester and A.J. are checking out Mark, believing him to be a realistic robot. Mark threatens to suck their brains out with bendy straws, but Chester and A.J. simply believe he is spewing Crash Nebula dialog, and are not afraid of him at all.
Vicky bursts into Timmy's room, shouting at the kids to keep it down. Timmy, Chester, and A.J. tremble in fear, but Mark is in awe of her ability to scare people. Her terrifying behavior is actually quite romantic to his kind. She drags Mark off to get rid of him, while shouting at the others to clean up the mess they made in Timmy's room. In outer space, Mark's parents were blasting their way through space, the Queen remarking that they wouldn't have to destroy so many planets in the way if they just asked for directions. The King and his wife squabble, while back on Earth their approach is noticed by Cosmo and Wanda.
Cosmo and Wanda tell Timmy that they have good news and bad news; the good news being that Mark is really an alien prince from the warrior planet of Yugopotamia. Timmy asks what the bad news was, but that really was the bad news, and the good news was that Cosmo found a nickel. Timmy tries to wish Mark back to his planet, but the wish does not work. Wanda reads from Da Rules and realizes that Mark is in love with Vicky, and their magic cannot interfere with true love. Chester and A.J. ask Timmy why he is talking to his goldfish, but he changes to the subject to Mark, saying that they had to get her away from Vicky, as she might sell him for makeup and other girl stuff.
Downstairs, Vicky threatens to take Mark's costume and sell it for makeup and other girl's stuff, but he is more interested in her. Vicky thinks he talks funny and asks him if he was from Europe. Mark tells her that he is a warrior prince from Yugopotamia, but Vicky simply thinks he is a foreign exchange student, and is disgusted by him. She orders him to make her a chocolate shake, which causes Mark to scream in fear. Chocolate is one of the deadliest substances to Yugopotamians, and her lack of fear towards it only makes Mark even more in love with her. In the kitchen, as Mark makes Vicky her drink, Chester and A.J. approach Mark in order to rescue him, but he tells them he does not want to be rescued, and then fires green goo at the boys to stick them to the wall, so that he can use their brains later on as gifts for Vicky. Timmy watches Mark's budding relationship with Vicky from upstairs, unable to fathom how anyone could fall in love with Vicky. Cosmo and Wanda check their wands and see the Yugopotamian fleet approaching. The Yugopotamians blow up Cosmo and Wanda's Mothership from earlier and set their sights on Earth. Timmy realizes he is out of time, and that he must speak to Mark's parents to see if they can talk some sense into their son.
Cosmo and Wanda poof Timmy to the King and Queen's ship, and they are stopped by a guard. They announce themselves as being from Earth, and that they wish to speak to the King and Queen. The guard says that they must pass three perils before they can do so. The three perils are skipping across a flower field, hugging a teddy bear, and eating chocolate; all of which are horrifying and deadly acts to Yugopotamians, but harmless and trivial to Timmy. The Yugopotamians see him as a fearless warrior, and the King and Queen cower in his presence. Timmy tells them that he has good news and bad news; the good news being that Cosmo named his nickel Philip, and the bad news (other Cosmo saying the nickel is a girl nickel) is that an Earth girl and Mark are falling in love, which Timmy will not stand for. The King and Queen agree to go to Earth and talk to Mark, so long as he does not eat any more chocolate in front of them.
Back on Earth, Mark returns to Chester and A.J. and tells them that things are not going so well between him and Vicky, so he is going to have to suck out their brains with straws and give them to her as gifts. Chester and A.J., still thinking Mark is a Crash Nebula-themed robot, play along with him by reciting lines from the earlier Crash Nebula episode. Timmy barges into the kitchen to save the day, but his purple water sprayer is not much of a weapon against Mark. Before Mark can get to Timmy however, Vicky calls Mark from the living room, his parents having arrived to collect him. They introduce themselves as the Changs (which would eventually become Mark's "official" last name on Earth in later episodes). Mark grabs and hugs Vicky, crying that he is in love with her, as she turns blue from lack of oxygen. The King is about to allow Mark what he wished, but he glances over and sees Timmy nearby, biting an eating a flower. The King fearfully tells Mark that it would not work out with Vicky since she is not of his kind, so Mark reluctantly lets Vicky go, and leaves with them in their spaceship.
Vicky follows the Changs outside and watches them blast off, shedding a tear for Mark and vowing to never forget him, although her dramatic moment abruptly ends when she finds Philip the Nickel on the ground. This causes Cosmo, miniaturized watching from Vicky's hair, to cry out in despair. Back indoors, Chester and A.J. compliment Timmy on the outstanding real-life game of Crash Nebula they played, and he thanks them. A narrator tells the audience "Will Timmy's secret ever be exposed? Will Cosmo and Philip the Nickel ever be reunited? Tune in next week for another exciting episode of... the Fairly OddParents!" as the scene zooms out to show three Yugopotamian children, watching Timmy, Cosmo, and Wanda on their television while eating cereal.