The Book: Peter Jones Arthur Dent: Simon Jones Ford Prefect/Frogstar Robot/Air Traffic Controller: Geoffrey McGivern Zaphod Beeblebrox: Mark Wing-Davey Marvin the Paranoid Android and Gag Halfrunt: Stephen Moore Arcturan Number One: Bill Paterson Arcturan Captain/Radio Voice/Receptionist/Lift: David Tate Roosta: Alan Ford Announcer (uncredited): John Marsh
The episode opens in the Hitchhiker's offices on Ursa Minor Beta, with a receptionist claiming that Zarniwoop, the editor of the guide, is too busy to take a call because he is both in his office, and on an intergalactic cruise.
It then moves to the bridge of a megafreighter that is due to land on Ursa Minor Beta. A crewmember denounces the Hitchhiker's Guide for being soft, and notes that he has heard they have created a whole artificial universe. Zaphod Beeblebrox is a hitch-hiker on the freighter, and as he listens to the radio, he hears a report that he has died, by being eaten by a Haggunenon. The manner of his escape is left unclear.
Meanwhile, Arthur and Ford are stuck in Earth's pre-history, drunk. As they discuss their predicament, they notice a spaceship half-appearing in front of them. They celebrate their rescue, and it vanishes. Eventually they deduce that this is a time paradox, and they need to figure out how to signal the ship in the future so they can be rescued. Following this is the Guide's entry on the subject of towels, making its first appearance.
On the ship, Zaphod explains to the crewmember that he is going to Ursa Minor Beta to find out what he's doing. He received a message from himself the previous night, telling him to see Zarniwoop in order to learn something to his disadvantage. Zaphod then explains how he escaped - the Haggunenon turned into an escape capsule before it got the chance to eat him.
Zaphod arrives at the Hitchhiker's offices, and demands to see Zarniwoop, but is given the same excuses as before. After revealing his identity, he is directed to Zarniwoop's office, and meets up with Marvin, who had also survived and coincidentally arrived at the same place. After Marvin persuades the lift to take them upwards, the building starts to shake, due to it being bombed.
Zaphod is met by Roosta, who blames the bombing on Zaphod failing to conceal his presence on the planet adequately. A Frogstar Robot class D soon arrives to come and get Zaphod. Zaphod orders Marvin to stop it (which he does, by tricking it into destroying the floor it is standing on), whilst Zaphod and Roosta escape into the pocket universe in Zarniwoop's office.
From the perspective of the three later radio series, all of the subsequent events of the Secondary Phase occur only in Zarniwoop's artificial universe, and not in the 'real' universe. They are later dismissed by Trillian as "psychotic episodes."
Eventually, the Frogstar Robots decide to take the entire building back to the Frogstar.