Synopsis
It has been revealed to Arthur that the earth has been built by the Magratheans and run by mice.
Other Archive resources

Hitch Hiker's Guide to the Galaxy (1981) | Episode 5
Having been blown up on the planet of Margrathea, Arthur, Ford, Trillian and Zaphod are mystified when they awake in restaurant at the End of the Universe.

Hitch Hiker's Guide to the Galaxy (1981) | Episode 4
Arthur discovers that mice are actually pan-dimensional beings, earth was a super computer to find the ultimate question and he's about to die.