Turlough sabotages the TARDIS, resulting in the appearance of a doorway which leads to an ageing spaceship. There the time travellers encounter the pirates Kari and Olvir, who realise that the vessel is carrying victims of the fatal and virulent Lazar disease. The ship docks at Terminus, a space station where the weary Vanir care for the Lazars in the last days of their lives. Soon Nyssa begins to succumb to the plague, while the Doctor discovers that Terminus lies at the exact centre of the universe. Meanwhile, in the heart of the Forbidden Zone, guarded by the mysterious Garm, waits an ancient and terrible secret...

Steve Gallagher's first Doctor Who story was Season Eighteen's Warriors' Gate. As it was entering production in the summer of 1980, Gallagher began discussing further ideas with script editor Christopher H Bidmead. They arrived at a narrative about a spaceship from another dimension which was equipped with an experimental Pandora Drive, the use of which had created the universe, and now had the potential to destroy it as well. The ship was tended by a religious order, and the sick made pilgrimages there in the hope of a cure. One of the priests had been transmuted into a minotaur-like figure; as a result, he was able to interact with entities from the other dimension, who operated at a different time scale and therefore moved almost inconceivably slowly.

Bidmead and producer John Nathan-Turner were both very happy with Warriors' Gate, and encouraged Gallagher to start working on this new concept. However, the better part of a year then passed without communication from the Doctor Who production team. The latter part of the development of Warriors' Gate had been fraught, and Gallagher began to assume that his proposal had been abandoned. Finally, on May 12th, 1981, an inquiry from Gallagher's agent prompted Nathan-Turner to apologise for the delay. He explained that the production office had been in a state of upheaval for several months, stemming from the replacement of Bidmead with Antony Root and then Eric Saward, as well as the overhaul of Doctor Who's principal cast -- most notably the departure of Tom Baker and the introduction of Peter Davison as the Fifth Doctor. Nathan-Turner assured Gallagher that interest persisted in his new story and, on August 4th, the writer met with Nathan-Turner and Saward to discuss its status.

Turlough's attempt to destroy the Doctor would meet with failure, but he would avoid casting suspicion on himself

At this point, the production team was in the midst of planning a trilogy which would form the core of Season Twenty, introducing a new companion named Turlough who would secretly be in the service of the evil Black Guardian. Nathan-Turner and Saward felt that Gallagher's idea was appropriate for the trilogy's second installment, in which Turlough's attempt to destroy the Doctor would meet with failure, but he would avoid casting suspicion on himself. Suitably amended, Gallagher's storyline was commissioned under the title Terminus on August 10th.

After delivering his story breakdown, Gallagher met again with the production team on October 14th. At this time, he was informed that Terminus would be the final story for Nyssa, a character Nathan-Turner felt had run its course. Gallagher was asked to provide a fitting swansong for Nyssa, placing more emphasis on the character than was usually the case. This decision was met with great disappointment by Davison, who deemed Nyssa to be the most appropriate companion for his Doctor and had lobbied to retain her. On October 15th, Gallagher was asked to proceed with the script for Episode One, although his formal commission did not come until November 3rd. The remaining installments of Terminus were requested on December 3rd.

In writing Terminus, Gallagher took inspiration from Norse mythology, naming the Vanir after a lesser group of fertility gods. Of the individual members, Bor was the father of Odin, head of the Norse pantheon; Sigurd was a great Norse hero, also known as Siegfried or Sivard Snarensvend; and Eirak was initially called Eirik, after a king of Norway and Northumbria also known as Eric Haraldsson or Eric Bloodaxe. Similarly, the Garm was named for a monstrous hellhound, also known as Garmr, who appeared during the time of Ragnarok, the twilight of the Norse gods. Meanwhile, the term Lazar was an archaic word for “leper”; it was derived from the Biblical figure of Lazarus, described in the Gospel Of John as having died from an illness, only to be resurrected four days later by Jesus.

Some elements of Gallagher's scripts changed over the course of their development during early 1982. The instability in the TARDIS was originally caused by an experiment Nyssa was conducting, rather than being Turlough's handiwork. Kari -- whose name was apparently Yoni until Saward observed that this was the Sanskrit word for the female reproductive organ -- contracted the Lazar disease in Episode Three. Bor initially perished in the same installment. Gallagher also wanted to hint at an underlying sexuality to the relationship between the Doctor and Nyssa.

The director assigned to Terminus was Mary Ridge, who had developed a good rapport with Nathan-Turner during his days as an assistant floor manager. Unfortunately, Ridge was confronted with trouble even before she officially started working on the serial. She had originally been allocated six studio days: a typical amount for a Doctor Who story with no location filming. However, an industrial dispute was brewing between the BBC and the electricians' union, resulting in a major reorganisation of shooting schedules. As a consequence, one of Ridge's studio days was clawed back, meaning that her team would be up against the clock to record Terminus.

Rod Vass thought that the Vanir armour was purely decorative, and was shocked that it was required for combat

More problems arose in the area of costume design. The fabrication of the Vanir armour was outsourced to Rod Vass of the props firm Imagineering, based in Witney, Oxfordshire. However, a miscommunication led Vass to understand that the armour was meant to be purely decorative; he was therefore shocked to learn upon delivery that it would be required for combat. The costumes proved to be extremely noisy when involved in vigorous activity, and costly refurbishing was required to address the problem. Ridge would also later claim that costume designer Dee Robson had crafted the outfits for Kari and Olvir in light blue, despite the fact that Ridge had made it known that this would interfere with effects work using the chroma key technique. According to Ridge, the costumes had to be remade in white, at significant expense. This account has been disputed by Robson, who has asserted that Kari and Olvir's costumes had always been white.

Production on Terminus began on September 28th, when model filming took place at BBC Television Centre Presentation Studio B in White City, London. September 29th and 30th were spent at the BBC Television Film Studios in Ealing, London, with Ridge focussing on the scenes involving Tegan and Turlough in the ductwork. Shortly thereafter, it was discovered that Episode One was underrunning, and Saward asked Gallagher to provide two new one-minute scenes. Unfortunately, Gallagher misinterpreted the request and instead extended several existing scenes to fill out two minutes' worth of material. Consequently, Gallagher's amendments were discarded. Around this time, he began working on a third Doctor Who proposal entitled “Nightmare Country”. However, it was deemed too costly to make, and so Terminus became Gallagher's last contribution to the programme.

The first studio session for Terminus took place at BBC Television Centre Studio 6 on October 11th and 12th, during which the production continued to be plagued by issues. On the first day, a power failure resulted in a two-hour delay; when the crew was finally ready to go, Ridge discovered that one set had been erected off its marks, incurring a further stoppage. Then, Nathan-Turner was forced to call a halt to the recording of scenes involving the interior of the TARDIS console because the correct circuitry was missing. This meant that Ridge had to record sequences on other sets which were not yet properly lit. Later, it was learned that neither of the drone robot props had been tested before being brought into the studio, and only one was found to work correctly. Despite these disruptions, Ridge was able to complete almost all of the material set within the TARDIS and the adjoining spaceship corridor.

More troubles arose the next day. Visual effects designer Peter Pegrum was responsible for Kari and Olvir's helmets, which he thought were only to be carried, and never worn. When Liza Goddard and Dominic Guard donned the headgear, they quickly found that a lack of air holes meant that the helmets easily fogged up, necessitating modification. Later, one of the extras playing a Lazar accidentally grabbed at Janet Fielding's top during a scene, causing the actress to expose herself.

Sarah Sutton was disappointed with her final story, and could not understand why Nyssa removed her skirt

Ridge spent the second day concentrating on material in the spaceship control room and various corridors, but was unable to complete everything she had planned. For the first time in her prolific career, Ridge was appalled to realise that she would have to delay some scenes until the already-packed second studio block. This resulted in an increasingly tense atmosphere on set, with Davison incensed that the actors' performances were being given short shrift in the rush to record. Sarah Sutton, meanwhile, was very disappointed with her final story, and could not understand the rationale for Nyssa removing her skirt.

For the second studio session, from October 25th to 27th, Terminus moved to TC8. Ridge began with some of the material in the spaceship corridor and lower deck which had not been completed in the first block. This included Nyssa's farewell, which Ridge had tried and failed to tape on the 12th by restaging it in the TARDIS console room -- a move the cast had felt was nonsensical. Originally, Nyssa and the Doctor were merely to shake hands as they parted, but Davison and Sutton decided that the Doctor should give Nyssa a kiss on the cheek instead. Next, Ridge moved onto scenes in the receiving area, the stockyard, the elevator and the depths of Terminus, alongside some of the material in the station's control room. Here, the pilot had been dressed with cobwebs; Davison objected, observing that he was not meant to be dead but rather moving very slowly, whereupon Ridge had them removed.

The sets for the Terminus control room and various corridors were used on both of the remaining days of the block. The middle day also saw the recording of scenes in the recovery room, the Vanir headquarters, the equipment store and the Lazar ward, while material in the damaged area and some additional modelwork were left for the last day. As time ticked away on October 27th, it looked as though an extra hour of recording time which Nathan-Turner had arranged beforehand would permit Ridge to complete Terminus. At the last minute, however, Nathan-Turner informed his director that she would not be able to have the additional hour after all, and a remount would be necessary.

Ridge was furious; the incident set a frost into her relationship with Nathan-Turner which would never completely thaw. Sutton was deeply disappointed by the development: after dealing with the high emotion of leaving Doctor Who, she would now have to come back and complete her last serial at a later date. Davison was also very frustrated with Nathan-Turner, and blamed his sour demeanour for casting a pall over Sutton's farewell party that night.

Terminus returned to the studio partway through the making of The King's Demons

It was now hoped that Terminus would be finished during the making of the next story, Enlightenment. However, some of the production dates for Enlightenment were themselves delayed until early 1983 because of industrial action by the electricians, and so Terminus ultimately returned to the studio on December 18th, partway through the making of The King's Demons. With Episode One still running short, the opportunity was taken to craft additional material involving Tegan and Turlough to open the story. The remaining scenes in the TARDIS console room and corridor, as well as those in the spaceship control room, were finally completed in TC1. Ridge was frustrated to discover that the spaceship set and a number of props had been mishandled in the interim, incurring damage.

Viewers in Wales got to see Terminus Episode One a day earlier than the rest of the country, as BBC Cymru's coverage of The Official Opening Of St David's Hall on February 15th prompted the region to bring Doctor Who forward to the 14th. For the rest of the United Kingdom, the Doctor's exploits were now airing five minutes later on Tuesdays, at 6.55pm. This was because Best Of The West, an American sitcom which had been scheduled after Doctor Who, had now been dropped, and the documentary series Vox Pop was moved up to replace it. On the 16th, Episode Two led into a special retrospective of BBC Children's programmes called In Front Of The Children; A Question Of Sport returned the following week. Even after its broadcast, one last issue remained to confront Terminus, as several individuals involved in leprosy awareness criticised the serial for promulgating archaic beliefs about the nature of the disease.

• Doctor Who Magazine #291, 31st May 2000, “Archive: Terminus” by Andrew Pixley, Panini UK Ltd.
• Doctor Who Magazine Special Edition #1, 2001, “Diamond Life” by Andrew Pixley, Panini Publishing Ltd.
• Doctor Who: The Complete History #37, 2017, “Story 126: Terminus”, edited by John Ainsworth, 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 Fifth Doctor by David J Howe and Stephen James Walker (1995), Virgin Publishing.
• In·Vision #66, July 1996, “Production” edited by Anthony Brown, Cybermark Services.