“If you spare this town from becoming a smoking hole in the ground, I'll try to be a better Christian. I don't know what I can do... Mm... Oh, the next time there's a canned food drive, I'll give the poor something they'd actually like, instead of old lima beans and pumpkin mix.”
"Homer Defined" is the fifth episode of Season 3. Basketball player Magic Johnson made a guest appearance in the episode as himself, becoming the first professional athlete to do so on the show. This episode was also the last episode to have Bart's chalk in the Opening Sequence squeak, hence the chalk gag, "I will not squeak chalk".
During a near-fatal meltdown at The Springfield Nuclear Power Plant, Homer frantically presses buttons on his console until he hits the right combination and saves the day. Homer becomes a hero even though he realizes in his heart that what he did was a fluke. Meanwhile, Bart's friendship with Milhouse becomes strained when Mrs. Van Houten won't let Milhouse hang out with Bart.
On the bus ride to the plant, Bart gives Milhouse one of a pair of Krusty walkie-talkies as a birthday present. Bart is crushed to discover that Milhouse has held a birthday party the previous Saturday, but he has not been invited. Milhouse seems hesitant to chat with Bart and avoids him for the rest of the day.
Meanwhile, at the plant, as Homer eats jelly donuts, one of them splatters onto a dial nearing the red zone. The plant is on the verge of a meltdown, and Homer seems to be the only person who can stop it. He has no skills and cannot remember any training (actually, according to a flashback, he never paid attention to the training as he was busy playing with a Rubik's Cube), however, and in desperation chooses a button via eeny, meeny, miny, moe. Miraculously, Homer presses the button that stops the meltdown; Springfield is saved, and Homer is honored as a hero.
Milhouse finally tells Bart why he was not invited to the party: Mrs. Van Houten thinks Bart is a bad influence on her son. She has ordered Milhouse to stay away from Bart, which he has reluctantly done. Suddenly deprived of his best friend, Bart resorts to playing with Maggie.
Mr. Burns rewards Homer for saving the plant with an "Employee of the Month" award (displacing longtime holder Smithers), a ham, a plaque, a discount coupon book, Burns' personal "thumbs-up", and a call from Magic Johnson. Even Lisa begins to admire Homer as a role model, but Homer's conscience haunts him. He knows (and fears that everyone else will realize) that his "heroism" was nothing but luck. Burns introduces Homer to Aristotle "Ari" Amadopolis, the owner of the Shelbyville Nuclear Power Plant. Ari wants Homer the hero to give a pep talk to his plant's lackluster workers. Homer is hesitant to accept, but Burns forces him into it.
Marge visits Milhouse's mother to try to repair their children's friendship. Marge admits that Bart really does influence Milhouse badly, but begs Mrs. Van Houten to let Bart and Milhouse be friends again. Upon realizing that both Bart and Milhouse are miserable without each other, his mother relents. At that rate, Milhouse invites Bart over to his house, and Bart happily pulls out a BB gun to play with.
As Homer gives his fumbling "motivational" speech, an impending meltdown threatens the Shelbyville plant. The crowd marches Homer to the control room, asking him to perform his heroic deeds once again. In front of everyone, Homer repeats his juvenile rhyme and presses a button blindly. By sheer dumb luck, he manages to avert this meltdown as well. He is even more widely derided as a lucky imbecile than he was hailed as a hero, and "to pull a Homer" becomes a widely-used phrase meaning "to succeed despite idiocy" (even entering the dictionary illustrated with a small portrait of Homer). However, the episode finishes with Lisa giving encouragement to Homer by saying "Our dad, now he belongs to the ages".