After soccer practice, Bart waits for Homer to pick him up, though his father has forgotten. When Homer finally remembers, he reasons to an angered Bart that they should just both admit they are wrong and try to put the issue behind them. Later, Bart views a commercial for a mentor program called The Bigger Brothers, which pairs up fatherless boys with positive male role models. Still angry at Homer, Bart goes to the agency pretending to be a young boy whose father was a drunken gambler who abandoned him. Barts story is so sad that the receptionist pairs him up with their best Bigger Brother, a military test pilot named Tom. The two spend time together doing a variety of activities, though Bart begins to feel guilty over taking up Tom's time despite not actually being fatherless. Eventually, Homer finds out about Bart's Bigger Brother and confronts Bart for it. Homer then decides to go to the Bigger Brothers Agency to get revenge by being assigned with a replacement son; a young poor boy named Pepi. Just like Tom and Bart, Homer and Pepi spend time together doing activities.
Later on, it is Bigger Brothers Day in Marine World, where the Bigger Brothers and their boys attend to celebrate (including Homer, Tom, Bart, and Pepi). After running into Homer, Tom begins to brawl with him, in a fight which rages across Springfield. In the end, Homer winds up getting poked on the back by a fire hydrant, breaking his spine, much to Tom's shock. As a result, Homer is sent to a hospital on a stretcher, and Bart holds himself responsible for this. Later on, Tom sadly talks about how much he will miss being a Bigger Brother, while Pepi is sad over losing his Bigger Brother. Fortunately, Bart suggests Tom become Pepi's big brother, to which they happily agree, and both Tom and Pepi walk out into the sunset holding hands. At the same time, Homer (whose back is now fixed) and Bart reconcile, as Homer teaches Bart how to brawl due to his experience with Tom.
In the subplot, Marge finds an anomalously high phone bill for calls made by Lisa to the Corey hotline — a premium rate phone service where television fans can listen to the voice of a fictional actor based on The Two Coreys. Lisa promises to stop increasing the family's phone bill, but continues to make calls to the hotline from such places as Doctor Hibbert's office and a telephone at Springfield Elementary. After Principal Skinner catches her, Marge suggests that Lisa try to go until midnight without calling the hotline; if she can do so, she will have conquered her addiction. Although tempted throughout the rest of the day, Lisa beats her addiction.