Miss Fowl's class is having their Christmas-themed show-and-tell, and Carl brings a bag containing an old Cheez-Nip snack. He explains that he left out a plate of Cheez-Nips for Santa Claus last Christmas Eve, and when he woke up the next morning, only one was left. However, Jimmy completely doubts that, as due to all the scientific improbabilities surrounding the character, he believes that Santa Claus does not really exist. Upon hearing Jimmy say this, Carl is greatly upset, and Cindy chastises Jimmy for hurting Carl's feelings, which he states was not his intention.
Later, in his lab, Jimmy apologizes for hurting Carl's feelings earlier and explains to Carl and Sheen why he stopped believing in Santa. Two years ago, Jimmy had asked Santa to bring him a core sample from Dwarf Star NG-7-38, but when he did not receive it, Jimmy became convinced that Santa was fake. Sheen, however, believes that Jimmy was just on Santa's naughty list that year. Just then, Jimmy's DNA tracker picks up a very strange signal from the Cheez-Nip snack Carl showed off earlier, and Jimmy states that the DNA must be from the saliva on the snack. Carl and Sheen believe that this must be Santa's saliva on the Cheez-Nip and, when Jimmy accidentally suggests it, they decide to go to the North Pole.
Over at Cindy's house, she and Libby are sneakily peeking at their Christmas presents when Cindy notices Jimmy, Carl, and Sheen preparing for their trip. Libby decides they should take an embarrassing video of Jimmy (using a camera they found in one of the gift boxes they were peeking at) to get back at him for hurting Carl's feelings earlier. While looking for something humiliating around Jimmy's rocket, they end up getting sucked into Jimmy's Hypercube. Unaware of the girls getting trapped in the Hypercube, Jimmy, Carl, and Sheen take off in Jimmy's rocket for the North Pole.
Shortly after arriving there, the boys find Santa's workshop in plain sight, but Jimmy thinks it is a cleverly-disguised army outpost. The doors then open and reveal the interior of the workshop to them. Unfortunately, Jimmy is still not convinced; he thinks the workshop is a glorified factory that parents order toys from, and that the elves are short people with an ear condition. Jimmy's DNA tracker then overloads and shoots a beam that reflects all over the factory and eventually hits Santa, scrambling his atoms. The chief elf, Lou, furiously tells Jimmy that he's now ruined Christmas because his "stupid scanner thing broke Santa." Cindy and Libby (who escaped from the Hypercube by turning up the volume on Libby's portable CD player) suddenly show up, having recorded video of this, and Cindy accuses Jimmy of trying to ruin Christmas for everyone else. As Cindy then starts describing a five-point plan to ruin Jimmy's reputation and save Christmas (though she hasn't yet figured out the latter part), Jimmy has one of the factory's toy rockets grab the girls and return them to Retroville.
Jimmy declares that he will deliver all of Santa's presents using science, and if he can do that, then it will prove there is no Santa Claus. With that, he stores all the presents in his Hybercube, builds some Christmas-themed upgrades to his rocket and, using a spare red Christmas light, installs a laser-guided navigational beacon on his robot dog Goddard's nose. Lou believes Jimmy is crazy for trying this, but he and his pals take off anyway.
Back in Retroville, Jimmy's parents, Hugh and Judy, see a news report on TV saying that Christmas has been cancelled due to Jimmy scrambling Santa's atoms (as shown in the footage Cindy provided). Upset that their son will now be reviled by everyone because of this, Hugh decides to invent a new holiday for people to celebrate, themed entirely around pies and called "Pule". However, Hugh's attempt to give out pies to everyone in Retroville ends in failure.
Meanwhile, Jimmy, Carl, and Sheen manage to deliver almost all of the presents within the whole evening, and when it seems they have finished, Carl is saddened by the apparent fact that Jimmy has proven his point. Jimmy then realizes that they have forgotten to deliver the presents meant for Retroville and gives his rocket a lightspeed blast from his warp module. However, the rocket goes so fast that it eventually breaks apart, and the boys go plummeting towards the ground; Carl, however, is delighted at this, since Jimmy actually failed to deliver all the presents and this means that Santa is real.
At that very moment, Santa shows up in his flying sleigh and picks them up with his tractor beam. Jimmy, finally seeing that Santa is real, is told that he has been on the naughty list for some time ("Told ya," remarks Sheen), and then apologizes for scrambling Santa's atoms. Santa then uses one of Jimmy's warp modules to speed up his sleigh (since it can handle going lightspeed better than Jimmy's rocket can) and delivers all the presents meant for Retroville (though he gives lumps of coal to Cindy and Libby) and also drops Jimmy, Carl, and Sheen off at their homes. After Santa departs, Jimmy goes to look under his family's tree and finds that Santa has given him the Dwarf Star sample that he wanted two years ago (it had needed time to cool off). Jimmy has Goddard place the Dwarf Star on top of the tree and then sings with his parents.
- A storybook adaptation of the episode was published by Simon Spotlight in October 2003, roughly two months before the episode aired. The book notably cuts out the subplot of Hugh inventing his pie-themed holiday, as well as Cindy and Libby's involvement in the story.
|Debi Derryberry||Jimmy Neutron|
|Frank Welker|| Goddard|
|Rob Paulsen|| Carl Wheezer|
|Jeff Garcia||Sheen Estevez|
|Carolyn Lawrence||Cindy Vortex|
|Crystal Scales||Libby Folfax|
|Mel Brooks||Santa Claus|
|Megan Cavanaugh||Judy Neutron|
|Mark DeCarlo||Hugh Neutron|
|Andrea Martin||Miss Fowl|
|Candi Milo||Nick Dean|
|Billy West|| Sam|
- Jimmy Neutron Wiki: Holly Jolly Jimmy
- "Holly Jolly Jimmy" at TV.com
- "Holly Jolly Jimmy" at the Internet Movie Database
- "Holly Jolly Jimmy" at the Big Cartoon DataBase