Bart, fed up with Homer's neglect, joins the Big Brother program posing as an abandoned child so he can hang out with a better father figure. Homer finds out about Bart's cool, new friend, Tom, and exacts his revenge by donating his time as a big brother to a real orphan named Pepi.
After playing soccer, Bart waits for Homer to pick him up. At the Simpson residence, Marge reminds Homer to go and get Bart on her way out the door—Homer says "I'm on my way", but unknown to Marge he is saying this because he is watching Wheel of Fortune and the exposed letters spell out "I'M ON MY WA*". Homer was so focused on the game show that he didn't hear what Marge said, and he forgets to pick up Bart. Bart is left alone as a storm approaches. Many occurrences at home remind Homer that he was meant to do something, but he cannot recall what. When Homer finally remembers after a dream about seeing Bart's skeleton on a soccer field, he rushes out to pick up Bart. Upon arriving, Homer finds Bart completely soaked from the storm that had past and his soccer ball had deflated over the time he had been waiting. Homer, knowing that Bart's anger is justified, carefully tries to put the issue behind them. But Bart is none the less furious at Homer for forgetting about him and refuses to even make eye contact with him. Bart then imagines Homer's face melting while he says "Now how bout a hug?".
When they return home, Bart watches TV when a television commercial for a mentor program called Bigger Brothers comes up. This gives him an idea and he goes to the Bigger Brothers Agency disguising himself with accent as a brave young boy whose father left him six years ago. Afterwards, Bart is assigned a big brother called Tom whom Bart first meets when he comes to school to pick Bart up by letting him ride on the back of his motorcycle. Later on, Bart and Tom meet up for Tomato Day at the Springfield Stadium (the purpose of the tomatoes is revealed when a recruiter for the Springfield Communist Party is introduced on the field before the start of the game; he is pelted with tomatoes before he can begin his speech, and remarks that it is at least better than "Dart Day"). Afterwards, they go to lift weights and watch Ren and Stimpy. Eventually, Homer finds out about Bart's Bigger Brother and angrily confronts him about the issue. Homer decides to go to the Bigger Brothers Agency to get revenge by being assigned a replacement son. There, he is assigned a child named Pepe (whom he calls "Pepsi" for a brief period). Homer shows Pepe the garage door, "a wonder of modern technology" and then the two look at the stars together.
Meanwhile back at the Simpsons' household, Marge finds a $378.53 phone bill for calls made to The Corey Hotline. Because of this, Marge heads up to talk to Lisa who is hiding in her room, as the entrance is decorated with a Corey poster. Marge tells Lisa that she understands what Lisa is going through and that when she was a girl she had a crush on a young man named Bobby Sherman. This revelation causes Lisa to laugh uproariously. Even so, in the end Lisa promises her mother "...you'll never be billed for another call." However, Lisa continues to make calls to the hotline from such places as Doctor Hibbert's office and from a phone at Springfield Elementary. After Principal Skinner catches her calling the hotline, he calls Marge. In Skinner's office, Marge suggests that Lisa try to go until 12 o'clock that evening without calling the hotline; if she can do so, she will have conquered her addiction. Lisa is eventually able to make it after a struggle.
Elsewhere, Homer takes Pepe to Marine World to attend Big Brothers Day. Tom also takes Bart there. After Homer runs into Bart, Tom tells Bart not to talk to strangers and begins to lead him away from Homer. Homer states that he is Bart's father. As Bart has told Tom many false or relatively over exaggerated stories of Homer being a terrible parent, Tom halts and asks Homer with barely-restrained anger "His father, the drunken gambler?" Homer seeing nothing wrong with the connection, instinctively and cheerfully replies, "That's right, and who might you be?" Tom punches Homer in the face, beginning a brawl between the two men. Homer manages to match Tom by fighting dirty; distracting Tom by saying a there's a troubled kid nearby and punching him when he looks away. The fight rages across Springfield, with Homer tackling Tom into a china shop, then sending him back out with an uppercut. At one point Homer and Tom tumble down one side of Springfield Gorge... and fight their way up the other side!
In the end, Tom stuns Homer with a series of punches which causes him to bend painfully backwards over a hydrant dislocating vertebrae in his spine and leaving him paralyzed. Homer ends up in a stretcher and Bart—who feels guilty for indirectly causing the fight—gets ready to ride with him to the hospital. Tom is left without a child to take care of and Pepe without a Big Brother. Seeing this, Bart makes an obvious conclusion, telling them that Tom should become Pepe's big brother. Tom and Pepe agree and start hanging out with each other. Afterwards, Bart and Homer reconcile and the episode finishes with them sitting on the couch, Homer teaching Bart how to fight dirty (like he did with Tom).
The writers wrote the role of Tom for actor Tom Cruise. However, when offered the part, Cruise repeatedly turned it down, so the producers used Phil Hartman instead. This is probably why Tom is an F-14 pilot, according to Bart. The writers based the Corey character on the actors Corey Feldman and Corey Haim, known as The Two Coreys. Pepe was based on the fictional character Dondi from the daily comic strip of the same name.
In the episode, Bart and Tom watch The Ren & Stimpy Show. The producers contacted Nickelodeon to get authorization to use the two characters for that sequence. Nickelodeon was strict about what The Simpsons was allowed to do, and the producers were not allowed to have the savageness that they wanted. The Ren & Stimpy Show's animators offered to do the layouts of Ren and Stimpy for the episode.
The television show Bart watches, Tuesday Night Live, is a parody of NBC's Saturday Night Live. Krusty appears in a sketch called "The Big Ear Family", and says that the sketch goes on for twelve more minutes, even though the joke's punchline has already been established. That was Jon Vitti's way of criticizing Saturday Night Live for having overlong sketches with thin joke premises. The sequence originally had a longer version of the Tuesday Night Live band playing into the commercial break, but it was cut because Vitti, who was a writer on Saturday Night Live during the 1985–1986 season along with fellow Simpsons writers, George Meyer and John Swartzwelder, did not want to come off as being bitter.
The writing staff was looking for a way to end the episode and executive producer Sam Simon suggested that they watch the film The Quiet Man. The writers came in on a Saturday to watch the film together. They were inspired by the film's fight scene between John Wayne and Victor McLaglen's characters to do a fight scene between Homer and Tom in the episode. The scene was difficult for the producers to sound-mix because they wanted it to be funny but not horrifying. They discovered that the more realistic the effects used sounded, the funnier the scene became. The producers tried all sorts of different sounds for when Homer cracks his back on the fire hydrant and chose the tiniest realistic sound, because they believed that it was the most painful and "hilarious".