The Doctor and Romana head to the planet Calufrax in search of the second segment of the Key To Time. Inexplicably, however, the TARDIS lands on Zanak, a world of seemingly limitless mineral wealth, ruled by the crazed Captain. Zanak is haunted by the Mentiads, a group of telepaths whose numbers swell each time a new golden age of prosperity is proclaimed. While Romana is captured by the Captain, the Doctor tries to help Mula, whose brother has been taken by the Mentiads. His investigation leads to the grim discovery that Zanak owes its riches to a wake of destruction on a planetary scale -- and to the deaths of billions.

During the spring of 1977, Douglas Adams was commissioned to write the pilot episode for a science-fiction radio comedy called The Hitchhiker's Guide To The Galaxy. He sent the script to the Doctor Who production office, where it prompted outgoing script editor Robert Holmes to arrange a meeting with Adams and his successor, Anthony Read. There, Adams was offered the opportunity to develop ideas for Doctor Who's sixteenth season, and he was made aware that each of its six adventures would be linked by the Doctor's search for the hidden segments of the Key To Time.

Adams' starting point was to consider how his narrative might be driven by the camouflaged nature of the segments. He suggested that one could be disguised as something large and important, forcing the Doctor to deal with the ramifications of reverting it back to its true form. Adams toyed with the notion of the segment being the Atlantic Ocean, or the Earth's Sun or Moon. However, his preference was for the segment to be revealed as the continent of Africa. To explain how a substitute Africa could be created, Adams developed the ancient intergalactic terraformers called the Forges of Bethsalamin; these ideas would later find their way into The Hitchhiker's Guide To The Galaxy instead. Another of Adams' ideas was that a segment might be disguised as a person, and this would later become a crucial element of the season finale, The Armageddon Factor.

Douglas Adams suggested that the segment of the Key To Time might be disguised as a piece of rubbish

However, it was a third approach which would ultimately inspire Adams to develop a storyline entitled “The Perfect Planet”. Aware that the TARDIS would be gaining a new occupant in the form of a brilliant but unworldly junior Time Lord -- ultimately Romana, although Adams dubbed the character Komnor and Gravity at different stages -- the writer anticipated that the Doctor would be eager to one-up his overly keen companion. As such, Adams suggested that the Doctor would find the segment of the Key To Time in the story's opening minutes, disguised as a piece of rubbish. He would conceal this knowledge from Romana, since he could then use the search for the segment as an excuse to investigate a mystery.

The bulk of “The Perfect Planet”, then, dealt with the Doctor trying to discover the origin of a new set of moons in orbit around the planet Jetral. He would learn that the Time Lords had once come to Jetral to mine a rare time crystal, and erected a giant totem which drained the aggression from its militant population, leaving them absurdly placid. However, the Time Lord Malchios, who had been despatched to deactivate the totem after the conclusion of the mining operation, instead became trapped within the mechanism. Over millennia, all of Jetral's malign emotions were absorbed into Malchios, and he was transformed into a psychopath bent on revenge against his people. Malchios used the mining equipment to hollow out Jetral -- with the slag forming the additional moons -- and used his amassed time crystals to turn the planet into a TARDIS. Malchios planned to materialise it around Gallifrey, allowing him to harness the power of the Time Lords and take over the universe. The Doctor used his own TARDIS to arrive in Gallifreyan airspace at the same time as Jetral, foiling Malchios' plans. Romana destroyed the travel mechanism, while the Doctor severed Malchios' link to the totem, ending his life.

Commenting on “The Perfect Planet”, producer Graham Williams observed that the notion of a device which drained aggression had recently appeared in The Sun Makers during Season Fifteen. He was also concerned that the Time Lords were becoming involved in too many Doctor Who storylines. In place of these elements, Williams suggested the inclusion of a space pirate character. This became the Captain; Adams also considered dubbing him the Admiral or the Skipper. Originally, the Captain had been exiled by the Time Lords to another universe, and was planning to return to the regular universe by teleporting an entire planet. With this new emphasis, the adventure was retitled The Pirate Planet by July; “The Pirates” may also have been considered.

Adams was also keen to feature a female villain, who would pose as a Nurse in service to the Captain. His first inclination was to reveal this character as the daughter of the Doctor's frequent Time Lord nemesis, the Master. Later, however, Adams concluded that this should simply be a female incarnation of the Master -- presaging a development which would finally manifest in Doctor Who some thirty-seven years later. The writer also considered the notion that the eponymous planet Zanak would be preying on worlds which had witnessed the Master's worst defeats. Eventually, however, it was decided to reduce the Time Lord presence in the narrative even further, and so the Nurse became the guise of the ancient Queen Ixoxaxox.

Douglas Adams intended to introduce a new TARDIS control room at the end of The Pirate Planet

Adams was commissioned to develop The Pirate Planet into a full storyline on July 18th. There was considerable rearranging of the supporting characters: Pralix's parents were originally Balaton and Kimus, and his friends were Mulov and Torrel. Balaton then became his grandfather and Kimus his brother, while Torrel was dropped. Finally, Mulov and Kimus' names were interchanged. Meanwhile, Adams devised the air car as a device he could employ to break up the monotony of scenes set in corridors. At this stage, Adams intended to introduce a new TARDIS control room at the end of The Pirate Planet. This would take the form of a conservatory looking onto manicured gardens, with the console resembling a sundial.

Adams was given the green light to turn The Pirate Planet into full scripts on October 20th. By now, however, he had also been contracted to provide five further episodes of The Hitchhiker's Guide To The Galaxy, and was producing Week Ending for BBC Radio Four. As a result, progress on The Pirate Planet slowed considerably, especially after Episode One was delivered to the production office in November. To make the Captain's scenes more interesting, Adams acted upon a suggestion from his half-brother, James Thrift, and introduced the Polyphase Avitron. For a time, he considered having the robotic parrot squawk lines like “Pieces of silicate!” The psychics initially known as the Mourners now became the Mentiads; Adams reused the name Komnor for one of their number. The reliance of the old queen -- now called Xanxia -- on the time dams to stave off her mortality was devised as an allegory for drug addiction, although its prominence was later diminished.

Dropped at this stage was the Doctor's imprisonment in the Captain's torture chamber, where he would have been subjected to horrifying visions -- one of which Adams had intended to be a Dalek. Also changed was the nature of the segment of the Key To Time. The storyline had already abandoned the notion of it being a common item -- at one stage, a drinking cup -- immediately recovered by the Doctor. Instead, its guise became a sacred jewel of Calufrax called the Janthras Stone. Now, however, Adams resurrected his early idea of the segment being camouflaged as something enormous, namely the planet Calufrax itself.

When Adams finally submitted his remaining scripts at the end of January 1978, Read discovered that they required a considerable amount of editing. They were still too long and too complex, and Adams' inexperience with television drama meant that he had little idea of what could be accomplished within the limitations of the Doctor Who budget. Fortunately, support arrived in the form of director Pennant Roberts, who had last worked on The Sun Makers. Roberts regularly looked for ways to add more female characters to his projects, and Pralix's brother Mulov accordingly became a sister, Mula.

Graeme MacDonald suggested that The Pirate Planet should be abandoned altogether

As Read and Roberts toiled to coax The Pirate Planet into a workable form, the BBC's Head of Serials, Graeme MacDonald, delivered a harshly critical verdict on Adams' scripts. In a March 14th memo, MacDonald suggested that the serial should be abandoned altogether; in particular, he disapproved of its strongly humorous bent. As with his similar reaction to The Invasion Of Time, the Season Fifteen finale, MacDonald's objections seemed to overlook the fact that Williams had decided to place a stronger emphasis on comedy in Doctor Who as a response to his superiors' instructions to steer the programme clear of the horror-tinged elements favoured by former producer Philip Hinchcliffe. MacDonald also noted his concern that The Pirate Planet squandered Romana's potential. This was a fate he felt had also befallen her predecessor, Leela, and which he was keen for the new character to avoid.

At the time, Williams was on leave while he recovered from a broken leg suffered during a February holiday in Madeira, Portugal. This left Read and Roberts to defend The Pirate Planet to MacDonald. They argued that there was insufficient time to develop replacement scripts, because the interconnectedness of the Key To Time story arc made it virtually impossible to rearrange the season's recording order. With just six weeks remaining before The Pirate Planet was due to enter production, MacDonald relented.

On April 17th, John Leeson was contracted to provide the voice of K·9 for The Pirate Planet. Two weeks later, on May 1st, location filming began with engine room scenes at Berkeley Nuclear Power Station in Berkeley, Gloucestershire. The rest of the location shoot took place in Wales. On May 2nd, the Mentiads marched across the countryside near Coity Mountain near Blaenavon; this was also the cliff upon which the Bridge sat. The attack on the Mentiads by the Captain's guards was staged at Bwlch y Garn in Ebbw Vale. It's likely that this was also the day that Roberts filmed minehead material at the Big Pit, a colliery in Blaenavon.

May 3rd was spent at the abandoned railway tunnels in Clydach Gorge, for scenes at the transporter tunnel. On the 4th, sequences at the base of the mineshaft were captured at Cathedral Cave, part of Dan-yr-Ogof, the National Showcaves Centre for Wales, in Abercraf. Cast and crew returned to Clydach Gorge on May 5th, and it may have been on this day that Roberts recorded the shots of Mula and K·9 traversing the countryside, on the grounds of the Monmouthshire Golf Club in Llanfoist.

The remainder of The Pirate Planet was taped at BBC Television Centre Studio 6 in White City, London, beginning with a two-day block on May 22nd and 23rd. The first day dealt with material on the city street and in Balaton's house, together with special effects sequences, while the second day saw recording on the sets for the Mentiads' chamber and the aircar, as well as model shots of the city. Scenes in the city square were completed on both days, as was some footage on the Bridge. On May 26th, model filming took place at Shepperton Studios in Shepperton, Surrey for the destruction of the Bridge.

The second studio session took place from June 3rd to 5th. Unfortunately, it witnessed a recurrence of the labour unrest which had plagued the two preceding Doctor Who serials: The Invasion Of Time and The Ribos Operation. This time, a dispute arose as to who was responsible for the operation of a caption scanner, and the resulting delays cascaded through the entire block. Further bedevilling Roberts' team was the theft of the Polyphase Avitron prop one night; fortunately, it was discovered hidden in a skip the following morning, averting further impact on the shooting schedule.

June 3rd and 4th dealt with the rest of the action on the Bridge and in the Mentiads' chamber. Some effects shots were taped on the first day as well, while the second day also encompassed recording in the inertialess corridor, the corridor outside the Bridge, and at the entrance to the engine room. June 5th was reserved for material in the TARDIS console room and limbo area, plus Xanxia's chamber, the trophy gallery, and the remaining special effects shots. The Doctor's fall against the TARDIS console was a late addition to the script to explain the facial injury sustained by Tom Baker while making The Ribos Operation. Vi Delmar agreed to remove her false teeth for her role as the methuselan Xanxia on this day -- but only after negotiating an extra fee. With time running short, Roberts was barely able to capture enough footage for the duel between the Polyphase Avitron and K·9 before the studio lights went dark.

• Doctor Who Magazine #253, 2nd July 1997, “Archive: The Pirate Planet” by Andrew Pixley, Marvel Comics UK Ltd.
• Doctor Who Magazine Special Edition #9, 22nd December 2004, “I'll Put You Together Again” by Andrew Pixley, Panini Publishing Ltd.
• Doctor Who: The Complete History #29, 2017, “Story 99: The Pirate Planet”, edited by John Ainsworth, Hachette Partworks Ltd.
• Doctor Who: The Handbook: The Fourth Doctor by David J Howe, Mark Stammers and Stephen James Walker (1992), Virgin Publishing.
• Doctor Who: The Pirate Planet by James Goss (2017), BBC Books.
• Doctor Who: The Seventies by David J Howe, Mark Stammers and Stephen James Walker (1994), Virgin Publishing.
• In·Vision #33, September 1991, “Production” edited by Justin Richards and Peter Anghelides, Cybermark Services.