The episode begins with Homer Simpson and his family enjoying a day at the Springfield Dog Show. Homer is excited to see the various breeds of dogs and is particularly interested in a dog named "Old Yeller." However, the family's attention quickly shifts when they see a dog that is a mix of various breeds, which they find amusing. Marge, on the other hand, is more focused on the competition and the potential for winning.

As the dog show progresses, the Simpson family becomes increasingly invested in the event. Bart, in particular, is drawn to a scrappy dog named "Sparky," who is not a purebred but has a lot of personality. Bart's affection for Sparky grows, and he decides he wants to adopt the dog. Marge is hesitant at first, concerned about the responsibilities of pet ownership, but Bart's enthusiasm convinces her to allow it.

After the dog show, Bart brings Sparky home, and the family begins to adjust to having a new pet. Initially, Sparky is a source of joy and excitement for the family, especially for Bart, who takes on the role of caretaker. However, as time goes on, Sparky's behavior becomes increasingly problematic. He chews on furniture, barks excessively, and causes chaos around the house. This leads to frustration for Marge and Homer, who are worried about the damage Sparky is causing.

In a pivotal moment, Marge and Homer decide that they can no longer keep Sparky due to his disruptive behavior. They sit Bart down to explain the situation, and Bart is devastated. He pleads with his parents to give Sparky another chance, but they remain firm in their decision. Bart feels betrayed and heartbroken, leading to a significant emotional conflict within the family.

Determined to prove that Sparky can be a good dog, Bart takes matters into his own hands. He begins training Sparky, using various techniques he learns from books and videos. Bart's dedication to Sparky is evident as he spends hours working with him, trying to curb his bad habits. This training montage showcases their growing bond and highlights Bart's determination to keep his new friend.

As Bart continues to train Sparky, he faces numerous challenges. There are moments of frustration when Sparky does not respond to commands, but Bart remains persistent. Eventually, Sparky begins to show improvement, and Bart's hope is reignited. He believes that he can change Sparky's behavior and prove to his parents that they should keep him.

The climax of the episode occurs when the family is invited to a local pet competition. Bart sees this as an opportunity to showcase Sparky's progress and win over his parents. He enters Sparky into the competition, and the family attends, albeit with some skepticism from Marge and Homer. During the event, Bart and Sparky face off against other dogs, including some well-trained purebreds.

As the competition unfolds, Sparky's antics initially cause chaos, leading to a series of comedic mishaps. However, in a surprising turn of events, Sparky manages to perform well in the final round, impressing the judges and the audience. Bart's hard work pays off, and he feels a sense of pride in Sparky's achievements.

In the end, the judges announce the winners, and while Sparky does not take home the top prize, he receives a special award for "Best Spirit." This recognition is enough to sway Marge and Homer, who finally see the value in Sparky beyond his misbehavior. They agree to keep him as part of the family, and Bart is overjoyed.

The episode concludes with the Simpson family celebrating Sparky's award, solidifying their bond with their new pet. Bart's determination and love for Sparky ultimately lead to a happy resolution, showcasing the importance of perseverance and the joy of companionship.

Homer feels ashamed of his cowardice after he is confronted by his son, Bart, who is disappointed in him for not standing up to a dog that is terrorizing the neighborhood. This moment of realization leads Homer to reflect on his own fears and insecurities.

In 'Old Yeller-Belly', Bart's relationship with Santa's Little Helper deepens as he tries to train the dog to be more courageous. Bart's determination to make his pet brave mirrors his own desire for approval from his father, leading to a heartfelt connection between them.

Homer's decision to confront his fears is triggered when he witnesses a series of events where he is unable to protect his family from a menacing dog. The culmination of his shame and the need to be a better father pushes him to take action.

Marge expresses concern and disappointment over Homer's cowardice, but she also supports him as he attempts to overcome his fears. Her reactions are a mix of frustration and encouragement, highlighting her role as a stabilizing force in the family.

Bart learns that bravery is not just about facing physical threats but also about standing up for what is right and being there for those you care about. His experiences with Santa's Little Helper and his father's struggles teach him the importance of courage in various forms.