Thirty years in the future Bart Simpson is going to die... that is, unless he undergoes radical transplant surgery. Bart's uncertain fate rests in the clouded memories of a Springfield not so long forgotten, a the generosity of an organ donor, and the love of his sister. Only Lisa can unlock the secret of Bart's shrouded past and solve the mystery. Her only clue: Bart's last conscious utterance - "Fish logs..."
Bart needs a transplant to survive 30 years in the future and is surrounded by his parents, Lisa, Maggie and her husband Gerald. Lisa is upset that all Bart says on his supposed deathbed "fish logs...". Lisa does go on a fact finding mission and talks to Milhouse who relays a story that Fat Tony was running from the cops and Bart protects him from Wiggum and in exchange, Fat Tony gives him a suitcase that Bart decides to open and finds fish logs, this causes issues with Skinner thinking Bart is selling illegal food and Martin who chokes on his food but Bart saves him. The power of fish logs entrances all the kids who buy Bart's food and not the cafeteria food which ticks off Superintendent Chalmers who tells SKinner that half the school's profits come from the cafeteria and the school could be going broke. Skinner tries everything to get the kids to go back to cafeteria food but Bart outwits him and he must release Lunchlady Doris.
At the same time, Mayor Quimby is angry that someone else has sold fish logs and wants Bart terminated or else Freddy Quimby loses his job. The influx of cash to do with the fish logs leads to bigger and better Springfield business. Not everything was rosy as Skinner had to close down the school to save costs, and then the domino effect happened as there's no legal way Bart can sell his fish logs and then the town goes to waste. Bart loses his fish log business, Mayor Quimby fired his nephew, Skinner realizes he closed down the school only to find out HE would not get any salary as well as the teachers.
After talking to Milhouse, Fat Tony and Ned Flanders, Lisa finds out the story but the kick was that SHE was out of town for the whole incident which was 2 weeks. Flanders relays that the state found out how bad Springfield was doing, gave the town an influx of cash to make sure "everything goes back to normal". Ironically, Ned is oblivious to his kids Rod and Todd cross dressing and needing estrogen shots. Lisa tries to relay her story with everyone about what Bart meant by "fish logs" but Bart is alive thanks to a transplant by Uter who after eating fish logs got himself buffed like Rainier Wolfcastle. Lisa is actually upset that Bart got away with a crime and it was a "selfish accident". Bart reveals that he was trying to beat a fish log eating record when he needed that transplant.