"What's The Difference?" is the twenty-fifth episode of Season 5.
Mark Chang seeks Timmy Turner's help after his fake-i-fier malfunctions and his evil fiancé Princess Mandie tracks him down to Dimmsdale Elementary School. To hide Mark, Timmy wishes the school into a puzzle book, but then Cosmo and Wanda lose their wands in the puzzle and worse, if Mandie doesn't find Mark then she will turn the whole school into a huge crater! Timmy and his godparents now must find the two wands before Mandie decides to obliterate the school.
Feeling bored from doing the same thing everyday, Timmy Turner decides to do something he has never done before--go to the school library. As expected, Timmy is totally bored since most of the books lack pictures. However, Cosmo then comes across a picture puzzle book in which they have to search for specific hidden objects that are hidden in the last place you would think to find it. Flipping through the colorful pages, Timmy is able to find all the hidden images, mainly because it was a book for three-year olds.
Suddenly, Mark Chang the alien comes bursting through the doors, worrying and screaming about how his Fake-i-fier was malfunctioning. Without his disguise, his fiance Princess Mandie would be able to quickly find him and forcibly marry him. Timmy calms the alien down and tells him that he can just wish the Fake-i-fier back to normal, but before he is able to, Princess Mandie appears and smashes through the doors of the library. She angrily grabs Mark Chang and prepares to blast him with a bazooka.
Unable to think rationally due to his panic, Timmy wishes that the whole school was laid out like his "Find Its" puzzle book. Everything becomes topsy-turvy. Globes become basketballs, atlases become boxes of cereal, lockers become milk cartons, and Mark Chang disappears in a cloud of dust, away from Princess Mandie. Realizing that Mark's disappearance from her clutches was because of Timmy's wish, she decides to get revenge and prepares to grab her bazooka to aim at him. However, much to her surprise, her bazooka has been replaced with a sausage because of the wish.
Even angrier than before, Mandie prepares to attack Timmy with her long, retractable claws, but Timmy distracts her and quickly hides, leaving Mandie to walk away, seething with rage. Wanda then calls to Timmy's attention that he could have just wished Princess Mandie away, and he attempts to do so. Unfortunately, after wishing that the school was just like the "Find Its" puzzle book, Cosmo and Wanda's wands have been replaced with turkey legs, so they have to find the wands.
Meanwhile, Crocker is in his room and it is shown that his coffee stirrer has been replaced with the wands. Somehow, Mr. Crocker doesn't notice even though the wand turned his desk into cheese and did some other strange and unexplainable things. Wielding a flaming sword, Princess Mandie continues her search for Mark Chang, and she stumbles into Principal Waxelplax's office. Waxelplax simply assumes that she is the new social studies teacher and states how she also keeps a medieval flail under her desk. As Mandie continues walking down the hallway, it can be seen by the audience that Mark Chang is hidden in the trophy case, his tentacles bent into the shape of the handles of a trophy.
Meanwhile, Timmy is still searching for the wands. Wanda then reminds him that just like the "Find Its" book, he has to look for the thing he's looking for in the place where he'd least expect to find it. After pondering for a moment, they decide to check out Crocker's room. However, Crocker was still in his room and unfortunately, Princess Mandie was nearby. Even though she is right next to the trophy case where Mark Chang was hiding, she is unable to find him and instead, mistakes a nearby octopus and a trash can for him, tackling them to the ground and beating them up in the process. She then notices Timmy and then demands for him to tell him where Mark is.
Timmy admits that he has no idea where, and she decides to use a bomb to turn Dimmsdale into nothing more than an empty crater when it explodes; that is, unless someone would sacrifice himself to be her husband. Entranced by Princess Mandie's aesthetic beauty, Cosmo and several other teachers try to go for her. Frustrated, Mandie screams that she wasn't talking about them. Unable to take the guilt, Mark Chang pops out from the trophy case and decides that he has no other choice but to marry her so that Dimmsdale would not be destroyed. However, despite Mark's sacrifice, Princess Mandie still took no mercy on Dimmsdale and continue letting the bomb count down to its destructive deed.
Timmy then bursts into Crocker's room and says that Princess Mandie, the new social studies teacher, just won an award for "best hunchback teacher who lives with his or her mother." Outraged, Crocker stomps out the room towards Princess Mandie, shouting about how he should have won. With Crocker's classroom all to themselves, Timmy, Wanda, and Cosmo search frantically for the wands. Timmy tells his fairy godparents to continue looking while he stirs Crocker's cup of cocoa with his fancy stirring stick. Through the window of the classroom door, Crocker can be seen chasing Mandie who is holding Mark Chang, now welded back into his trophy shape. He furiously shouts at her to give him his "trophy."
Much like Crocker, Timmy at first fails to realize that the coffee stirring stick is a wand. Meanwhile, through the window of the classroom door, Mandie and Crocker continue fighting over the "trophy," both pulling viciously on Mark's "shiny handles." Finally, Timmy discovers that the fancy coffee stirring stick was the wand(because the cocoa was magically delicious) and he gives the wand to Wanda, who then wishes for Cosmo to find his wand. Timmy then wishes for Mandie to be back on her planet and for everything to not be a "Find-it" anymore.
With everything back to normal and Mandie not on his track, Mark Chang, back in his human form again, thanks Timmy for all his help. Becoming curious, Timmy then asks Mark what happened to his image fake-i-fier in the first place that caused it to short out. Mark states that he doesn't know, but he assures Timmy that it wouldn't happen again. All of a sudden, Trixie approaches Mark, stating that he is cute. She then blows Mark a kiss, causing his fake-i-fier to go haywire yet again, turning him into several objects and ultimately a jelly donut. The food-loving Principal Waxelplax then appears and grabs Mark, thinking he is an actual jelly donut, and she prepares to eat him.