Milhouse comes over with a bike modification kit, which they use on Bart's bike to make it look cooler. While riding the modified bike, they are hassled by older boys with "big boy" bikes. It makes Bart wish for a ten-speed bike. To get a new bike Bart sacrifices his bike in front of Dr. Hibbert's Mercedes. Snowball II is then run over by the Hibbert Mercedes and the family buries the pet in the backyard.
Bart and Homer get Bart's new bike, but it needs to be assembled and Homer tries to do his best, but the bike falls apart when Bart tries to show it off to the older boys. Bart and Homer are watching "Robot Rumble" and the father and son teams inspire Homer to build a robot for them to enter in competition. Meanwhile, Marge and Lisa look for a new cat and she finds a new one that she calls Snowball III, however it soon drowns in the fish tank. Bart wakes to find a new robot in his room, which is actually Homer inside of a robot looking suit.
Bart competes on "Robot Rumble," with the robot he's called "Chief Knock-A-Homer," but Homer is nowhere to be found. Homer, hidden inside the suit, manages to win his first match, but only after he receives many cuts and bruises. Lisa gets and quickly loses a new cat named Coltrane.
Chief Knock-A-Homer quickly works his way to the finals, but Bart is sorry that his father hasn't been able to see any of the Chief's victories. The Chief's final match is schedules to be against Professor Frink and his son's deadly looking robot. Lisa's depressed about her propensity to kill cats, is surprised when a crazy lady leaves her with a new cat. Lisa sees that new cat looks kill proof, and decides to call it Snowball II and forgot the whole dead cat thing ever happened.
After the first round of the finals Bart discovers the secret inside of "Chief Knock-A-Homer" and thinks his dad is even cooler for doing that. The match is stopped in the second round when Homer's presence in the robot is revealed to everyone and the Frink robot ultimately loses the match to man.