The Traken Union is governed by a Keeper gifted with the fantastic powers of the Source. The current Keeper's abilities are waning as he nears the end of his thousand-year tenure, and he asks the Doctor and Adric -- who have escaped from E-Space -- to stop an evil he believes has taken root on Traken. But the statue-like Melkur has already corrupted Kassia, one of the ruling Consuls. The Doctor and Adric stand accused of murder, and are saved only by the intervention of Kassia's husband, Consul Tremas, and his daughter, Nyssa. Together, they must unmask the villain behind the Melkur and safeguard the Source.

Christopher H Bidmead became Doctor Who's script editor at the start of 1980, but he was not producer John Nathan-Turner's first choice. This was Johnny Byrne, a regular writer for All Creatures Great And Small, on which Nathan-Turner had been the production unit manager. Byrne was not willing to relocate from Norfolk to London in order to work on Doctor Who, but he did indicate his interest in providing scripts for the series. This led to a meeting between Bidmead and Byrne around the spring of 1980. Byrne suggested a story about millennialism: the belief that a period of cataclysm and upheaval takes place every thousand years, as espoused by Zoroastrianism and by some Christian sects. With only twenty years left until the year 2000, Byrne felt that this was becoming a timely and interesting topic, and he wanted to interlace it with the tumult that sometimes results when a long-serving head of state dies or retires.

Byrne was commissioned to prepare a storyline for The Keeper Of Traken in early June, and the four scripts were then requested on July 18th. Byrne initially depicted a mediaeval society, divided between the scientific Greys led by Hellas, and the zealous Blacks under Inquisitor General Zorca. Zorca summoned a being called Mogen which he believed to be a demon, but who was actually the last survivor of a race of super-beings with fantastic mental abilities. Mogen wanted to take control of the powerful Source, and make Traken a stepping stone to galactic conquest. Zorca framed Adric for murder, and Episode Two's cliffhanger originally involved the Doctor, Adric and Hellas on the brink of execution, about to be crushed between blocks of steel. A key element of Episode Four was a stolen component from the TARDIS, which Mogen used to construct a time disintegrator. Byrne also introduced Hellas' daughter, Nyssa, whom he named for a friend called Nerissa.

John Nathan-Turner was concerned that viewers would no longer accept a change of lead actor, given Tom Baker's 7-year tenure

The Keeper Of Traken was positioned as the penultimate serial of Doctor Who's eighteenth season. The production team suspected that Tom Baker would be leaving the programme at the end of the year, having grown increasingly unhappy with the changes Nathan-Turner had introduced. But while the producer agreed that it was time for a new Doctor, he was very concerned that viewers would no longer accept a change of lead actor, given Baker's unprecedented seven-year tenure. To this end, he wanted to reintroduce a popular element of the programme's past, in order to bridge the changeover from Baker to his successor. Since the Doctor's Time Lord companion, Romana, would be leaving Doctor Who partway through Season Eighteen in Warriors' Gate -- the story that would precede The Keeper Of Traken -- he thought to bring back a former companion for two or three adventures.

As such, in June, Nathan-Turner contacted Elisabeth Sladen, who had played Sarah Jane Smith from 1973 to 1976. When Sladen declined the invitation, the producer turned to Louise Jameson; as Leela, she had been Baker's co-star in 1977 and 1978. Nathan-Turner was mindful that, although the robot dog K·9 would be exiting Doctor Who along with Romana in Warriors' Gate, the version of the character left with Leela on Gallifrey -- in Season Fifteen's The Invasion Of Time -- could also be reintroduced. Jameson was initially disinterested in returning to Doctor Who, but she later had a change of heart and indicated her willingness to come back for two stories. By this time, however, Nathan-Turner had decided that he wanted Leela to accompany the new Doctor throughout Season Nineteen, a scenario which Jameson rejected.

Having failed in his efforts to bring back an old friend of the Doctor's, Nathan-Turner instead decided to reintroduce an old enemy. This was the Master, an evil Time Lord who had originally been played by Roger Delgado from 1971 until the actor's untimely death in 1973. The Master had already been resurrected in 1976's The Deadly Assassin, with Peter Pratt playing a version of the character in a condition of near-complete physical deterioration. Nathan-Turner now wanted to restore the Master to an echo of Delgado's incarnation -- albeit in a less humorous and more malevolent form.

Nathan-Turner and Bidmead felt that The Keeper Of Traken was eminently suitable as a vehicle to reintroduce the Master. He could easily replace Mogen, while the powers of the Source would explain the villain's transformation from his cadaverous state to a rejuvenated body. This turn of events would also presage the Doctor's own imminent regeneration. The new Master would then appear in both Baker's final adventure and the first story to feature the Fifth Doctor, forming a loose trilogy to guide the audience through the major upheaval of Baker's departure.

Mogen's role was largely filled by the Melkur, to keep the true villain's identity a surprise until the final episode

In late August, Byrne revised The Keeper Of Traken to incorporate the Master; by this time, Baker had confirmed his intention to leave Doctor Who at the season's end. Mogen's role was largely filled by the statue-like Melkur, in order to keep the true villain's identity a surprise until the final episode. Byrne had a great interest in Irish mythology, and the inspiration for the Melkur's collar came from the Jodhan Moran or Moran's Collar, which was worn by a legendary judge so certain of his righteousness that the collar would strangle him if he ever made an unjust decree.

Byrne then left on vacation, giving Bidmead permission to make any further changes he deemed necessary. The script editor subsequently excised the Grey and Black factions -- thereby avoiding similarities to the Savants and the Deons from Meglos, earlier in the season -- and replaced Hellas and Zorca with the married couple Tremas and Kassia. The name Tremas was chosen to be an anagram of “Master” at Nathan-Turner's insistence, although Bidmead felt that this element was illogical.

To play the revitalised Master, Nathan-Turner recruited Anthony Ainley, with whom he had worked on The Pallisers, and who had been cast by executive producer Barry Letts in an adaptation of Nicholas Nickleby. On September 12th, Ainley was contracted to appear in the final eight episodes of Season Eighteen, with an option for as many as eight more during Season Nineteen. Ainley agreed to Nathan-Turner's suggestion that he view some of Delgado's episodes, but the producer subsequently failed to make the necessary arrangements.

Meanwhile, Nathan-Turner had become very keen on Nyssa. He suggested that she be retained as a companion for at least a few stories, providing the audience with another familiar face in the wake of the Doctor's regeneration. This was in spite of the fact that the introduction of an additional companion, Tegan Jovanka, was already being planned for the season finale, Logopolis. Byrne agreed to the use of Nyssa beyond The Keeper Of Traken, although he would retain his copyright on the character. Bidmead was sceptical of Nathan-Turner's last-minute decision-making, but he agreed to flesh out Byrne's original concept. In the process, some early ideas were lost, such as Nyssa exhibiting a preternatural sensitivity.

The task of finding an actress to play Nyssa fell to director John Black. He had been appointed to The Keeper Of Traken on the recommendation of his girlfriend, costume designer Amy Roberts. Black selected Sarah Sutton, a former child actress who was now seeking more mature roles. On October 9th, Sutton's original contract for The Keeper Of Traken was extended to include an option for up to twenty-eight additional episodes. It was decided that Nyssa would not join the Doctor at the end of The Keeper Of Traken, but would instead be reintroduced in Logopolis if Sutton's option was taken up. A character description for Nyssa was added to the Doctor Who Writers' Guide on October 30th.

Geoffrey Beevers (the Master) was the husband of Caroline John, who had portrayed companion Liz Shaw in 1970

The Melkur costume was a collaboration between Roberts and designer Tony Burrough. It was based upon Umberto Boccioni's 1913 sculpture Forme uniche della continuità nello spazio (that is, Unique Forms Of Continuity In Space). Since strong vocal skills would be essential for the part, Black cast Geoffrey Beevers as the decayed Master. Beevers was the husband of Caroline John, who had portrayed companion Liz Shaw in 1970; he had appeared alongside his wife as Private Johnson in The Ambassadors Of Death. During rehearsals, Robin Soans sought a motivation for the tendency of his character, Luvic, to speak more rarely than the other Consuls. He and Black agreed that Soans could play the role with a stammer, but this was vetoed by Nathan-Turner.

Recording for The Keeper Of Traken began with a three-day session from November 5th to 7th at BBC Television Centre Studio 6 in White City, London. The first day dealt with material in the courtyard and in the TARDIS console room. Baker was in a dour mood: although his romantic relationship with Romana actress Lalla Ward was going through a rough patch, Baker nonetheless missed her presence on set, and he disliked being surrounded by so many newcomers. During supper, Nathan-Turner confirmed to Sutton that the option on her contract had been invoked. The second day saw the completion of scenes in the Grove, along with model shots. The last day of the block was spent on sequences in Tremas' and Seron's chambers, as well as those in the corridors.

The second studio block was held in TC8, and was scheduled to run from November 21st to 23rd. It came on the heels of the surprise announcement on the 19th that Baker and Ward were engaged and planned to marry during December. As a result, press interest in the production was unusually high. Reports citing Sutton's addition to the regular cast also began to appear on the 21st. The first two days of the session were dedicated to scenes in the Keeper's sanctum and the sanctum antechamber, with some material in the service vault also taped on the opening day. The Master costume from The Deadly Assassin was refurbished for Beevers' use, although the mask was altered so that more of the actor's face was visible. Unfortunately, a vortex machine meant to overlay a tornado effect on the climactic sequence broke down shortly before recording, and so basic wind machines had to be employed instead.

A sudden strike by BBC electricians led to the cancellation of the final studio day

Work on The Keeper Of Traken then ground to an abrupt halt, when a sudden strike by BBC electricians over a parking dispute led to the cancellation of the serial's final studio day. Acting quickly, Nathan-Turner managed to schedule a replacement date on December 17th in TC6, during location filming for the season finale, Logopolis. The remaining sequences in the service vault were completed, alongside those in the cell and the adjoining corridor, plus the Melkur control room.

Meanwhile, Nathan-Turner had begun the search for a new script editor to replace Bidmead, who would be leaving Doctor Who at the end of 1980. He approached Ted Rhodes, who was the script editor on All Creatures Great And Small, but Rhodes was not interested in moving to Doctor Who. To ease the transition between Bidmead and his successor, a trainee named Antony Root was assigned to Doctor Who. He had previously worked, uncredited, on Destiny Of The Daleks as an assistant floor manager. Seeking a more ambitious position, Root had trained to be a script editor and was attached to the BBC's Script Unit, where he had impressed Bidmead with his critique of unsolicited Doctor Who submissions. Root joined the production team during November for a three-month stint.

• Doctor Who Magazine #236, 13th March 1996, “Archive: The Keeper Of Traken” by Andrew Pixley, Marvel Comics UK Ltd.
• Doctor Who Magazine Special Edition #9, 22nd December 2004, “Another One Bites The Dust” by Andrew Pixley, Panini Publishing Ltd.
• Doctor Who: The Complete History #33, 2017, “Story 114: The Keeper Of Traken”, edited by Mark Wright, Hachette Partworks Ltd.
• Doctor Who: The Eighties by David J Howe, Mark Stammers and Stephen James Walker (1996), Virgin Publishing.
• Doctor Who: The Handbook: The Fourth Doctor by David J Howe, Mark Stammers and Stephen James Walker (1992), Virgin Publishing.
• In·Vision #51, July 1994, “Production” edited by Justin Richards and Peter Anghelides, Cybermark Services.