As Marge drives the kids to school, Bart and Lisa start fighting with each other. Distracted, Marge rear-ends the car ahead of her. Homer takes the car to a garage, where a guy named Mike gives him a loaner luxury sedan. Homer falls in love with his fancy wheels. At school Bart tries to impress a new, tough-looking kid named Donny. Bart jumps on the end of a seesaw, intending to hurl a garbage bag into the air. The ploy backfires, and Bart is pelted with debris. Bart tells Homer that everyone at school thinks Donny is cooler than him. Homer encourages Bart not to give up. Homer adjusts the air-conditioning controls in the loaner, and creates his own weather system; including a miniature tornado. As Skinner plays basketball in the school gymnasium, Bart makes his way to the boy’s locker room and slips metal steel-toe inserts into Skinner’s shoes. When Skinner addresses students in the auditorium, Bart climbs beneath the stage and uses magnets to control Skinner’s feet, making him do odd-looking movements. The kids erupt with laughter. Bart forces Skinner out the back door, and into a large bin marked “lost retainers.” Skinner vows to catch the culprit who humiliated him. Bart reacts with surprise when Donny steps forward, and takes the blame. Bart doesn’t know Donny is a snitch hired by Skinner and Chalmers to collect evidence on Bart so he can be expelled once and for all.

When Skinner is finished “punishing” Donny, Bart invites him to his tree house where they eat blue licorice. Donny remarks that he’s never seen blue vines before. Bart says they’re only sold in Europe, and sticks a few extras in Donny’s shirt pocket. When Lisa tries to enter the tree house, Bart and his friends douse her with fruit juice. At school some kids distract Skinner so Bart and Donny can put frozen cockroaches in the faculty lounge microwave. Bart reacts with shock when Skinner catches them in the act. When Skinner foils prank after prank, Bart realizes something isn’t right. Groundskeeper Willie, who has no love for Skinner, tells Bart there’s a rat at work; but Willie doesn’t know his identity. Bart begins trailing a kid he believes is the snitch. It turns out to be Milhouse. Bart and his friends force Milhouse into a locker in the middle of a field, and leave him there. Cletus mistakes the locker for an outhouse. Homer receives word that his old car has been repaired. Homer makes his way to the garage to pick it up. Reluctant to give up his loaner, Homer sabotages his car so he can keep the luxury sedan.

Believing he’s rid the school of its “rat” problem, Bart plans a new prank involving an ostrich egg and Skinner’s deck enclosure. Meanwhile, Homer takes Lisa for a ride in the loaner. He tells her he was supposed to return the vehicle weeks earlier. He notices his old car for sale at a dealership. Overwhelmed with feelings of nostalgia, Homer turns in the loaner, and gets his old car back. Bart notices that Skinner’s tongue is stained blue… the same color as the rare licorice he shared with Donny. Bart realizes Donny is the snitch. Bart and his friends lure Donny to a storage warehouse, where they intend to drown him in a mixture of Mentos and Diet Coke. Suddenly Skinner, Chalmers, and Willie enter the warehouse. Bart realizes Willie betrayed him. Skinner and Chalmers announce that Bart is being sent to a juvenile detention center in international waters. Suddenly Donny shoves a hand-truck full of Mentos into some Diet Coke, triggering a massive explosion of foam. Bart and Donny escape to the roof, where Donny says he’ll do what he’s always done: survive.