The story's about a young Mariah Carey (voiced by Breanna Yde), who has always wanted a dog and has asked for one pretty much every single Christmas for as long as she can remember, but has never gotten it. When two of Mariah's friends (who both have dogs) ask for her help with a charity fashion show that they're organizing, Mariah agrees to help them before they inform her that they're "short one girl with a dog." Now Mariah doesn't just want a dog—she needs a dog.
Later on, Mariah sees a puppy named "Princess" at a pet store and decides that she wants to adopt her—however, since having a pet is pretty big responsibility, Mariah has to prove to her parents that she can handle taking care of a dog before actually adopting one. So to prove that, she agrees to dog-sit her Uncle Reggie's dog, Jack, who proves to be a scraggly little rascal—in fact, he's considered the worst dog in the county! Jack turns Mariah's family's perfect holiday preparations upside down in hilarious ways.
While the holiday isn't exactly the Christmas that Mariah wished for, it ends up being more than she ever could've wanted.
The movie features examples of:
- And Starring: This applies to Henry Winkler, who gets And Henry Winkler as Grandpa Bill .
- Calling the Old Man Out: Inverted. Lucy and Bill are not at all pleased with their son's lying about Jack to trick Mariah out of wanting a dog.
- Disney Acid Sequence: Mariah experiences this as she sees Princess and experiences life with her.
- Everyone Has Standards: Grandpa Bill might be a heinous prankster, but even he doesn't approve of his son's plan of giving Mariah a stray dog in hopes of it changing her mind about wanting a dog for Christmas.
- The Film of the Song: This film is one of Mariah's "All I Want For Christmas Is You".
- Jerk with a Heart of Gold: Young Mariah is a generally good natured kid even if she's prone to stubborn and selfish moments.
- Narrative Backpedaling: Jack performing all sorts of tricks at the dog show is immediately revealed to merely be Mariah's Imagine Spot.
- Troublemaking New Pet: While Jack really isn't a "bad" dog, he's still pretty rambunctious and causes quite a bit of trouble for Mariah and her family when they first take him in.
- Wanting Is Better Than Having: Mariah comes to realize that owning a puppy is hard work when taking care of Jack.