Principal Skinner is going away to a principal's convention and wants to win the "Disciplinarian of the Year Award." However, he starts to not trust anyone about keeping a statue of the puma mascot safe. The next morning, everyone is locked out with Principal Skinner gone with his keys, until Groundskeeper Willie opens up the school. But once they get inside, something huge has happened: someone has stolen the puma statue! The people who were missing at the time of the crime were Jimbo, Dolph, Kearney, Martin, Mrs. Krabappel, Groundskeeper Willie, Milhouse and Bart.
Mrs. Krabappel is the most determined person to find it, not wanting to be transferred to East Springfield Vocational Training School. Suddenly, everyone hears a moan coming from a locker, only to be Milhouse, who was stuffed into a locker at the end of the day before and was there the whole night. Edna suspects him and Bart to have stolen the statue. They tell her and Willie it is at the Nuclear Waste Treatment Center, allowing the two to escape. While walking home, Wendell approaches Bart with a water gun, telling him the "fat boy" wants to see him. He is later to be revealed as Martin, who wanted to steal the statue. He asked Jimbo to take the puma so he would bring it to the city on Jebediah Springfield Day and be a hero for returning a paint-covered, jewel-encrusted treasure which was to be raffled. But Jimbo never returned, making Martin think he betrayed him, and asks Bart to help him get it back.
Bart returns home and asks Lisa for help in getting the puma back to the school and clearing his name. She believes his innocence and heads to the school to find any evidence. Meanwhile, Bart goes to the Kwik-E-Mart to find out if the bullies know anything about the disappearance. Lisa discovers Miss Hoover taking a file out of a cabinet in Principal Skinner's office. She also, finds a piece of paper in his trash. Lisa brings it home and it is revealed to have been a list of Skinner's enemies, but threw it out after spilling coffee on it. Bart also says the bullies were stuffing tires into the coolant intake vents at the Nuclear Power Plant. Lisa decides to round up the suspects and "grill em."
The next morning, before Skinner comes back, all the suspects arrive to his office. Lisa first suspects Mrs. Krabappel, who she claims was jealous of Skinner's position. Willie supports this theory, but is also accused, since he had to polish it everyday. Nelson laughs at him, but Lisa calls him out, saying Skinner had given him numerous detentions. She also accuses Martin and Jimbo, because of their deal. Lastly, Lisa accuses Miss Hoover, whose aunt was mauled by a puma, and the statue would remind her of the tragedy. Despite all this, she reveals that the real culprit is Principal Skinner. He returns with the statue since he kept it with him for safekeeping. He also reveals to have gotten 3rd runner up in the contest. Willie puts the puma back where it belongs and everything goes back to normal.
Later that night, Martin sneaks into the school and removes part of the paint on the statue, only to have been made out of plaster and not jewels, causing the bullies to stuff him in a locker.