500 Keys

Plot

The Simpson family returns from an errand to find Maggie locked in the car. As they hunt for a spare key, Maggie frees herself, and the family discovers a set of keys that open every door in Springfield. At school, Lisa uses one of the keys to uncover a hidden classroom. She tells Principal Skinner about it, but when she returns with the school newspaper, the room is concealed by a bookshelf.

Skinner and Superintendent Chalmers take the key from Lisa. She gets a copy made and finds the classroom behind the flimsy bookshelf, where a shadowy figure writes "The children are on Bus 23" on the chalkboard. Meanwhile, Bart uses the keys to cause chaos but accidentally performs good deeds, earning the key to the city. Marge and Maggie find a key for a wind-up toy that makes farting noises as it moves.

The toy escapes, and they chase it across town. Homer uses a key to enter the Duff brewery with Barney and takes the Duff blimp for a joyride. To learn more, Lisa and Bart ask Nelson, who explains that Bus 23 was a bus full of children that drove over an ice bridge and never returned. Homer flies them in the blimp to the river where the ice bridge once stood.

Lisa falls into the water and sees the submerged Bus 23; Homer dives in to save her. Inside the bus, they discover the children are mannequins. The wind-up toy rescues them by knocking over a tree, which they grab onto. The mysterious figure is revealed to be Otto, who drove Bus 23 and is relieved he was not responsible for any children's deaths.

Bart forces Chalmers and Skinner to confess everything. Years ago, the school received a grant to improve classrooms. Skinner cashed the check but left the money in his pants pocket, and his mother destroyed it in the laundry. To hide the loss from the government, Chalmers and Skinner built a fake classroom with rented mannequins and photographed it.

They could only afford to rent the mannequins for one day and had to return them by 5:00 PM to avoid an extra charge, as the rental company did not prorate. While Otto drove the mannequins to the rental office in Bus 23, the ice bridge collapsed, and the bus sank into the river.

Chalmers and Skinner apologize to Otto for letting him believe he had killed the students. Later, Otto drives his bus across an icy bridge, thinking the real children he is transporting are actually mannequins. The bus falls into the river.

Production

Albert Brooks reprises his role as Hank Scorpio from the eighth season episode "You Only Move Twice" in a cameo. The blackboard gag corrects a previous mistake: in "Homer Scissorhands," guest star Kristen Schaal's surname was misspelled as "Schall" in the credits. Schaal thanked the producers on Twitter for fixing it. The gag reading "It's 'Schaal', not 'Schall'" aired only in the televised version; streaming services like Hulu and Disney+, as well as reruns, instead show "Guinea pigs should not be used as guinea pigs." The closing credits feature the sound of jingling keys, followed by a solo violin performance of the show's theme.

Reception

When "500 Keys" first aired in the United States on May 15, 2011, around 6 million households tuned in. Among adults aged 18 to 49, the episode earned a 2.5 rating and a 7 share, meaning it captured 2.5% of that age group and 7% of those watching TV at that time. Its ratings were flat compared to the prior episode, "Homer Scissorhands." The A.V. Club's Rowan Kaiser found the episode "amusing" but said it "never comes near great stuff," calling it "disposable" and giving it a B. TV Fanatic's Eric Hochberger rated it 4 out of 5 stars, praising the storylines for Lisa and Homer while noting that the plots for Marge and Bart were less engaging.