It has been revealed to Arthur that the Earth has been built by the Magratheans and run by mice. Meanwhile his companions have been suddenly confronted by something nasty (probably certain death).

Slartibartfast takes Arthur to his study and shows him a film which explains the story behind the quest to find 'The Ultimate Question'.

The story begins with a race of hyper-intelligent pan-dimensional beings building a super-computer called 'Deep Thought' to calculate the Ultimate Answer of Life, the Universe and Everything. After 7.5 million years, it announced the answer - 42.

Deep Thought then said that in order to find the Ultimate Question, that would explain the Ultimate Answer, an even larger computer needed to be built. 'Deep Thought' called this the 'The Earth'... and it turns out The Vogons demolished the computer just five minutes before the final question to ask was due to be given.

Arthur and Slartibartfast then meet up with Ford, Zaphod and Trillian, who are unharmed after having been attacked. They also meet Trillian's mice, who are two of the pan-dimensional beings who designed the experiment. They cannot be bothered to go through the whole experiment again and so decide not to build a second Earth.

Their discussion is interrupted by the police wishing to arrest Zaphod. Arthur, Ford, Zaphod and Trillian try to confront them, but the police instead shoot them, until they blow up a computer bank that the four where hiding behind.