The episode opens with a guide entry explaining the legendary planet of Magrathea, which manufactured planets millions of years ago, until the galactic economy collapsed. Zaphod has been explaining to Ford that he has found the legendary planet of Magrathea, whilst Trillian tends to a pair of white mice. Zaphod orders the computer to land on the planet surface.
Before long, they receive a transmission from the commercial council of Magrathea, informing them that the planet is closed for business and asking them to leave. They ignore this and later receive another message, noting that nuclear missiles have been sent at the ship. Attempts to evade the missiles fail, and Arthur uses the ship's infinite improbability drive, which ends up turning the missiles into a very surprised looking whale and a bowl of petunias. Trillian discovers that during the chaos, her mice escaped.