Bart gets into a fight with Nelson Muntz, the school bully, while defending Lisa and the cupcakes that she baked for Miss Hoover. Nelson beats up Bart after school and warns him to expect the same treatment the following day.
At home, Marge consoles and encourages a crying Bart to reason with Nelson. Homer takes Bart away from Marge and says, "Well, thank you very much, Mrs. Maharishi Gandhi!" Marge angrily sighs at Homer. Homer then urges Bart to bend the rules and fight dirty. Taking Homer's advice, Bart is beaten up again. Bart turns to the toughest member of the Simpson family, Grampa Simpson, who introduces Bart to Herman, the crazed one-armed proprietor of an army surplus store. He instructs Bart on military tactics, then Bart declares war on Nelson and his sidekicks.
Bart enlists Nelson's other victims in his army and trains them for combat. Herman commands from Bart's treehouse as Bart leads his forces into battle. Ambushing Nelson and his sidekicks, they commence saturation bombing with water balloons. Nelson's thugs surrender, and Nelson is taken prisoner. He threatens to beat up Bart as soon as he is untied. Herman drafts the armistice treaty, which states that Nelson will retain his position and name, but will not hold any actual power. Then, Bart and Nelson sign the treaty. Then, Marge enters with cupcakes, and peace prevails.