Arthur Dent wakes up to find that his house is about to be bulldozed, and his day is only going to get worse. At the pub his friend Ford Prefect tells him that he is an alien and the Earth is about to be destroyed to make way for a new hyperspace bypass. Will Ford and Arthur escape Earth in time?

Arthur, Ford, Zaphod, Trillian and Marvin travel with the Heart of Gold to the legendary planet, Magrathea, the home of the planet builders. They land on the planet and set off to explore. Zaphod, Trillian and Ford explore beneath the surface, where they make a surprising discovery... Meanwhile, Arthur and Marvin are approached on the surface by Slartibartfast, who explains that the Earth was destroyed 5 minutes too early, and they intend to build a new one...