At a church picnic, Bart and the other kids play "Capture the Flag" together. When Rod Flanders picks Ned to be on his team, Bart picks Homer to be on his. In a mad dash to bring the flag back to their side, Homer collapses, too out of shape to run a short distance. Bart feels humiliated

Homer starts an exercise regimen at night, keeping his efforts secret from the family. He starts eating Powersauce sports bar and joins a gym. There, he runs into Rainier Wolfcastle, who starts training him. After two months of working out, Homer is thinner and stronger. At the gym, two Powersauce execs try to draft Wolfcastle into climbing the tallest mountain in Springfield, the Murderhorn, as a Powersauce publicity stunt. Wolfcastle refuses. Bart, overhearing the conversation, has them approach Homer. Homer accepts, not wanting to disappoint Bart. Grampa tries to warn him off the expedition, recounting his own adventure on the Murderhorn and the betrayal of his climbing partner, McAllister.

The execs partner him with two Sherpas to make sure that Homer gets to the top. By day, Homer makes little progress up the mountain, but when Homer wakes up at night and discovers the Sherpas dragging him up the mountain, he fires them and goes for the top, solo. After a long climb, he reaches a plateau, thinking he has reached the peak, only to discover he still has a long climb ahead. Homer crawls into a cave for shelter and discovers that frozen body of C.W. McAllister along with evidence that it was Grampa who betrayed him. Giving up, Homer nails a flag on the ledge. The flagpole creates a crack that topples the rest of the mountain, making where Homer stands the top of the mountain. When Homer gets down, using the frozen body as a makeshift sled, Bart tells him that he’s the coolest dad ever.