The starship Heart of Gold is headed for the planet Magrathea, a planet which it is generally agreed does not exist. In trying to land on Magrathea's surface, the crew faces an ancient nuclear missile defence system, escaping only when Arthur turns on the Infinite Improbability Drive. This helpfully replaces the missiles with a bowl of petunias and a very surprised sperm whale, who learns about the ground before he hits it. Later on, deep in the core of the planet, an unknown enemy attacks Trillian, Zaphod and Ford while Arthur meets Slartibartfast, an old man who designs planets for a living. Slartibartfast takes Arthur on a tour of the factory floor, showing off his latest project - Planet Earth, Mark Two.
