"They Saved Lisa's Brain" is the twenty-second episode of Season 10.
Lisa is invited to join the local MENSA society after penning an inspiring letter over Springfield's complete humiliation at the hands of her father.
The citizens of Springfield take part in a contest hosted by KBBL Radio to see who can do the stupidest thing. Lisa, who is forced by Marge to watch, is very disgusted by this as it shows how dumb the town is, especially with participants like Bart swallowing various objects, Barney belching after drinking an entire six pack of Duff and Homer singing while dressed in a suit made of popcorn kernels and popping them with hair dryers. After the judges reveal the winner, themselves for watching the contestants make spectacles of themselves, the participants revolt and start a riot. Lisa is disgusted and writes a letter to the newspaper criticizing the town's lack of refinement. Lisa's letter is published, but she is annoyed when no one will read it. She receives a letter to go to a house for a secret meeting. Upon visiting the place, she is welcomed as a member of Springfield's MENSA chapter, a group of highly intelligent people. Among them are Principal Skinner, Dr. Hibbert, Comic Book Guy, Professor Frink and Lindsey Naegle.
During a recreation of the renaissance in Springfield Park, their gazebo is unrightfully being used by Lenny, Carl, Barney, Sam and Larry, who stand around drinking and tell Principal Skinner to beat it when he says that MENSA booked the gazebo. When the group complains to Chief Wiggum, he ignores them and joins the others in drinking. Outraged that, as Dr. Hibbert puts it, "they live in a town where the smartest have no power and the stupidest run everything", they confront Mayor Quimby for their grievances, who mistakenly thinks they found stolen lottery money and flees town indefinitely. Now without a leader, the group consult the city's constitution, which allows for the most educated citizens to run office on his behalf. The newly appointed leaders then take this opportunity to make beneficial changes to Springfield, including euphemizing jury duty to "the Justice Squadron" to encourage more people to attend, remove the green light from the traffic lights and implementing clocks to run on the metric system. However, their governance starts crumbling when each member selfishly chooses to pass laws on their own without consulting with the others. During a town meeting in the park, they openly argue about which laws ought to be passed, when Stephen Hawking makes a surprise visit and criticizes their falling utopia. The town falls into a riot and Hawking reassures Lisa that sometimes even the most intelligent are fallible, except him, of course. Marge tells Lisa that everyone has a different idea of the perfect world, only to be caught by Hawking reading that message off his computer screen.
In the subplot, Homer steals a prize from the gross-out contest and gets a coupon for a free pornographic photo session. He shows his pictures to Marge, but to his dismay, she is more fascinated by the background setting than Homer's sex appeal.