The Simpsons go to Shelbyville to see a musical. The musical paints Shelbyvillians as smart, sophisticated people and Springfielders as hicks and morons. After the play, a furious Lisa declares that Springfield is not nearly as fitting of the Shelbyville stereotype as suggested, and an equally angered Marge goes to Springfield's Cultural Advisory Board to brainstorm a plan to make Springfield more sophisticated. During a free word association, Marge gets the idea to create a concert hall and hire Frank Gehry to build it. Gehry refuses at first, but is soon inspired after he crumples Marge's letter and hurls it to the ground. The $30 million project is eventually finished, but opening night proves to be a bust when everyone in Springfield leaves after hearing the first five notes of Beethoven's Fifth Symphony. Not even the symphony sticks around after Marge tells them about the next performance: an atonal piece by Philip Glass.
At the town meeting the next day, Mayor Quimby realized that the town hated classical music and called the people 'stupid hicks' for not telling him that in the first place. Mr. Burns swoops in with an idea of his own: take over the space and turn it into a state prison. Homer applies for a job as a guard, but is rejected after Otto switches his thoroughly drug-laded urine sample with Homer's and Mr. Burns has a despondent Homer kicked out of the interview room. To make more money off the prison, Mr. Burns forces Chief Wiggum to reinstate old and forgotten laws in order to fill his prison with convicts. Homer becomes one of those convicts after getting caught kicking a can five times down the street (which, according to an old law, is considered illegal transportation of litter).
Homer is sent to work in the prison kitchen—and becomes a prison snitch after unwittingly alerting the guards of Snake's escape attempt. Soon, Homer is rewarded with food, special treatment, and a new plasma TV, while the other prisoners try to find out who keeps ratting out their secret plans (which is made easy after Homer admits to Marge that he is being paid to snitch in the visitation room, something his solid-gold "Snitch Life" pendant confirms). The other prisoners get wind of this, and stage a plan to get back at Homer. In the prison library, Snake tells Homer about an upcoming breakout, and Homer passes this to the guards. While all of the guards wait outside for the breakout, the prisoners attack Homer. Using the key to the concert hall given to her as head of the Springfield Cultural Activities Board, Marge finds Homer in the prison kitchen with the other prisoners close on his tail. They take refuge in the gas chamber, where Marge scolds Homer about the lives he ruined with his tattling. Before the prisoners can attack Homer and Marge, the guards come in with tear gas and riot gear. As they are released, Homer uses his snitching for good by telling Governor Mary Bailey (last seen on "Bart vs. Lisa vs. the Third Grade") about the prison's deplorable conditions and food. Eventually, Homer is released and the governor tells the prisoners that, since there is no room left in the prisons they were transferred from, they will be put on a garbage barge and bare-knuckle box until someone emerges as their king, a plan the hardened convicts applaud. Marge is glad that Homer is out of prison, and Homer heads out to Moe's after she falls asleep, where he finds an obese Snowball II and tells her not to breathe a word about Homer going to Moe's.
Meanwhile, Bart and Lisa find out that Snowball II has been gaining weight. Initially in denial, Lisa soon decides to follow her and discovers she has been regularly visiting and eating food from another family, who believe she is theirs and nicknamed her "Smokey". Snowball prefers her second family to the Simpsons, to Lisa's dismay. Bart goes in to set the record straight, but instead the family fills him up with good food and teaches him the same trick they had taught Snowball.
During the end credits, Homer runs into the concert hall, claiming the building is a death trap. Bart tells Homer that the entire scene is a dream conjured up by Homer's mind after he fell asleep watching The Towering Inferno, at which point Homer asks Bart how he knows the name of his prophetic vision.