The Simpsons travel to Shelbyville, where they tour the theater district. Marge takes an interest in a musical called “Song of Shelbyville.” The play, it turns out, is filled with anti-Springfield sentiment, and compares its residents to “stupid hicks.” As the shocked Simpsons leave the theater, snooty theatergoers hoot at them. During a meeting of the Springfield Cultural Activities Board, Marge and her fellow board members agree that something must be done to rectify Springfield’s image. They decide to contact famed architect Frank Gehry in hopes of convincing him to build a concert hall in Springfield just like he did in Los Angeles. When Gehry receives the board’s letter, he rolls his eyes and crumples it up into a ball. Then he stares at the crumpled-up ball and is suddenly inspired. He designs a new concert hall for Springfield based on the crumpled-up paper. Unfortunately the residents of Springfield are unimpressed with the highbrow symphony orchestra chosen to play at the concert hall. The hall loses money and is forced to close. When creditors dog city hall to repay the loan used to build the hall, Mayor Quimby announces that the city is completely broke. Then Mr. Burns steps forward and offers to purchase the concert hall, erasing the city’s debt. Left with little choice, Quimby turns the building over to Burns, who intends to turn the structure into a state prison. Meanwhile Lisa is puzzled by Snowball II’s sudden weight gain.

Homer applies for high-paying prison-guard job. He interviews with Officer Krackney, who says all Homer needs to do is pass a drug test. He hands Homer a plastic cup. Unfortunately Otto switches his cup with Homer’s. When Mr. Burns receives the results of “Homer’s” test — which is riddled with drugs — he’s disgusted. Lisa and Bart grow convinced that Snowball is eating food somewhere else. They decide to spy on the cat to see where the food is coming from. Eventually Snowball leads them to a house where a loving mother greets the cat. Lisa and Bart realize that Snowball has a secret life with another family. Mr. Burns grows impatient when the prison operates at a mere ninety-nine percent capacity. Wiggum proposes enforcing arcane laws to fill the prison. He arrests Homer for violating an outdated law involving the number of times someone can kick a can. Homer is transported to prison, where he’s stripped of his clothing and sprayed with a high-pressure hose. Later, while working kitchen detail, Homer witnesses Snake attempt an escape by climbing into a garbage truck. Concerned for Snake’s safety, Homer alerts the guards. Impressed, Officer Krackney offers Homer a job as a snitch. Meanwhile, when Snowball II returns home, Lisa tries to win her back with some cat toys. Snowball II runs off.

Before long Homer is tattling on his fellow inmates, including Fat Tony and his fellow mobsters, and being rewarded with gifts. Lisa follows Snowball II to the other family’s house, where she’s amazed to find out the cat knows how to do tricks, and goes by the name “Smokey.” She’s dismayed when the cat snarls and scratches at her. Back at the prison Fat Tony instructs his men to find out who’s been leaking information to prison guards. When Marge visits Homer in prison, Homer presents her with a gift from Tiffany’s, and tells her about his lucrative position as prison snitch. Marge blurts out that Homer is a snitch, catching the attention of other inmates. When Fat Tony learns the truth, he announces that Homer must die. Later Snake tells Homer about an upcoming jailbreak. Homer relays the information to Officer Krackney. It turns out, however, that Snake leaked phony information as a diversion. As the prisoners close in on Homer’s cell, Homer attempts a getaway using a Segway. He smashes through a railing along a prison balcony and falls. Homer turns up inside the prison kitchen, where Marge is waiting. Suddenly the doors burst open and Fat Tony and his men enter. Homer and Marge take refuge inside a gas chamber. Guards fire gas canisters into the prison, causing the prisoners to lose consciousness… except for Homer and Marge, who are protected by the sealed gas chamber. Marge convinces the governor to give the prisoners a reprieve by sending them to a garbage barge. Bart enters the house of Snowball’s other family to find out why the cat hangs out there. When Bart leaves the house, he excitedly tells Lisa about all the things inside, and how he learned new tricks. Lisa rolls her eyes. That night Homer sneaks out of the house and makes his way to Moe’s bar. Along the way he encounters Snowball II. Homer promises to keep their midnight excursions a secret.