While Homer takes the Duff Blimp for a joyride, Lisa discovers a secret room in the basement of Sprinfield Elementary School.



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Episode cast overview:
Homer Simpson / Wiseguy / Guy with a letter / Barney Gumble / Gil Gunderson / Mayor Quimby / Key Man (voice)
Marge Simpson (voice)
Bart Simpson / Todd Flanders / Nelson Muntz / Ralph Wiggum / Joe Spuckler (voice)
Lisa Simpson (voice)
Hank Scorpio (voice) (as A. Brooks)
Additional Voices (voice)


Barney accidentally made Homer ride on the Duff Blimp for a joke. Meanwhile, Lisa finds a secret key to a hidden room at Springfield Elementary School; it is not what she expects at all but, she soon finds out a school mystery about a bus and some children.

Plot Summary | Add Synopsis


Animation | Comedy





Release Date:

15 May 2011 (USA)  »

Filming Locations:

Company Credits

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Technical Specs


Sound Mix:


Aspect Ratio:

1.78 : 1
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Did You Know?


When Homer is driving through "Suicidal Moron Pass", the license plate on the front of the car is NABF14, the production code for this episode. See more »


Nelson Muntz: Yeah, I've been held back more times than I can count, which is probably why I got held back so many times.
See more »


References Avatar: The Last Airbender (2005) See more »


Bridal Chorus
Composed by Richard Wagner
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User Reviews

A Clever, Different Format for an Episode,
3 November 2011 | by (Ireland) – See all my reviews

500 keys is a fantastic Simpsons episode with a very well written storyline and loads of very funny scenes. The format of the episode is very clever and unique, it separates all five Simpsons members out in to four stories, which all come together very nicely in the end, they were all very enjoyable, Lisa's one was complicated and detailed, while Homer's was mostly comedy, it was a risky and different episode that worked. The only thing about the episode that I found a little unfulfilling was Bart's story, it was quite funny and entertaining while it lasts but it draws to a conclusion too quickly, he eventually gets involved with Lisa's story but I would have been happy if the plot in which he struggles to cause trouble was more developed. Lisa's plot is definitely the best, it was very cleverly devised, it plays out like an actual detective mystery, with twists and turns throughout and a pleasing conclusion, definitely the main reason why this episode is so great, but Homer travelling through Springfield on a blimp never failed to make me smile and laugh. Funny and very unique, 500 Keys is definitely one of the highlights of the twenty second season.

When Marge finds a large collection of keys, she separates it among the family members to see what they find.

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