When asked to produce the Ultimate Question, Deep Thought says that it cannot; however, it can help to design an even more powerful computer that can. This new computer will incorporate living beings into the "computational matrix" and will run for ten million years. The computer is revealed as being the planet Earth, with its pan-dimensional creators assuming the form of white lab mice to observe its running. The process is hindered after eight million years by the unexpected arrival on Earth of the Golgafrinchans, and is then ruined completely, five minutes prior to completion, when the Earth is destroyed by the Vogons to supposedly make way for a new hyperspace bypass.
Come on the Vogons, we need you ASAP.