Arthur and Ford have been discovered. Vogon Captain Jeltz tortures them by reading his poetry. He then has Arthur and Ford thrown off his ship, to what must be certain death - except for one improbable miracle. At the last second, an infinite-improbability prototype ship (which can pass through every point in the Universe) rescues them. What is rather surprising is that Zaphod Beeblebrox, the hip cat who stole the spaceship, is vaguely familiar to Arthur. And so is Zaphod's companion, Trillian.

Fortune is on the crews' side - the transporter on the ship is still working, but needs someone to manually operate it. Marvin is therefore pressed into volunteering to sacrifice himself so the rest of the group can escape. Arthur and Ford get separated from Zaphod and Trillian and find themselves on board a space ship about to crashland into the prehistoric past of a planet that the two of them find strangely familiar. If this is indeed Earth, then history as they know it is about to be changed - and so is the Ultimate Question to Life, the Universe and Everything....