To make the case for the defence at his trial, the Doctor presents an adventure from his future, when a distress call summons the TARDIS to the space liner Hyperion III. His new companion, Melanie, witnesses a crewmember die in the booby-trapped Hydroponics Centre, only for the body to disappear. The Doctor unmasks an alien Mogarian as an undercover agent -- who is promptly murdered. The ruthless Professor Lasky and her team are keeping secrets in an isolation room. Lurking in the shadows are the sinister plant-like Vervoids. And, in the courtroom, the Doctor realises that the evidence is being manipulated...

Once it was agreed that Peri Brown would be written out of Doctor Who midway through Season Twenty-Three, a new companion was required. As such, producer John Nathan-Turner and script editor Eric Saward developed Melanie Bush, a computer programmer from Pease Pottage, West Sussex, whom the producer insisted should be red-headed. Inspired by the workout craze which had recently been popularised by celebrities such as Jane Fonda, Mel would be a vocal proponent of fitness and healthy eating. Although she would exhibit a strong feminist streak, it could wax and wane depending on the situation. An outline for Melanie was disseminated on July 5th, 1985. It noted that she would be the first British companion in many years; since the departure of Sarah Jane Smith in 1976, the Doctor had travelled with a succession of aliens, Australians and Americans.

By this time, Nathan-Turner and Saward had decided to construct Season Twenty-Three around a year-long story arc in which the Doctor was put on trial by the Time Lords. The evidence would take the form of the Doctor's adventures, drawn from his past, present and future in the manner of Charles Dickens' 1846 novel A Christmas Carol. Melanie would be introduced as a “future” companion in the ninth episode. Consequently, the incident which brought her into the Doctor's orbit would never be depicted, although the outline posited that she had helped prevent the Master from committing computer fraud on a worldwide scale.

The four episodes forming the “future” segment would be comprised of a linked pair of two-part serials

Despite the fact that the BBC had reduced Season Twenty-Three to just fourteen episodes, Nathan-Turner and Saward were keen to wring as many “first nights” as possible out of the schedule, since a story's opening installment often provided a bump in the viewing figures. With this in mind, it was decided that the four episodes forming the “future” segment of the season would be comprised of a linked pair of two-part serials. They would take place in the same location and share many of the same sets; a similar strategy had previously been employed for 1975's The Ark In Space and Revenge Of The Cybermen. Assigned to develop these narratives were David Halliwell and Jack Trevor Story, both veteran writers but newcomers to Doctor Who.

Unfortunately, Story struggled mightily with his serial, entitled “The Second Coming”. Halliwell, on the other hand, progressed quickly on “Attack From The Mind”, only for Saward to become disenchanted with his work. In mid-October, both serials were abandoned, and it was decided that the “future” segment would now consist of just a single four-part narrative. Recognising that Halliwell and Story's lack of experience on Doctor Who had contributed to their difficulties, the production team approached former script editor Christopher H Bidmead. Bidmead had mostly recently contributed 1984's Frontios, although his “The Hollows Of Time” had been a casualty of the BBC's directive to overhaul the original plans for Season Twenty-Three.

Bidmead began developing an adventure called “Pinacotheca”. Cognisant that he was working to a tight deadline, he corresponded regularly with Saward to ensure that his work was satisfactory. As such, both he and Nathan-Turner were shocked when, in early February 1986, Saward pronounced “Pinacotheca” boring and unusable. With a new set of scripts now urgently required, Saward contacted Sapphire & Steel creator PJ Hammond, whose involvement was suggested by the production office's former continuity adviser, Ian Levine. Hammond quickly began writing “Paradise Five”. This time, however, it was Nathan-Turner who was unhappy with the results, and Hammond's script was dropped towards the end of February.

Some thought was then given to asking Robert Holmes to write the “future” segment. He had already scripted the “past” narrative, “The Mysterious Planet”, and was then working on the two-part season finale, “Time Inc”. However, Holmes was contending with significant health problems, while BBC Head of Drama Jonathan Powell had demanded substantial rewrites on “The Mysterious Planet”. As a result, it was almost immediately obvious that Holmes was in no position to develop four additional scripts at very short notice.

On March 1st, John Nathan-Turner ran into writers Pip and Jane Baker in a lift at BBC Television Centre

Then, on March 1st, Nathan-Turner ran into writers Pip and Jane Baker in a lift at BBC Television Centre in White City, London. The Bakers had written 1985's The Mark Of The Rani, and had briefly been tasked with a story entitled “Gallifrey” for Season Twenty-Three, before it was rendered defunct by the development of the trial storyline. Nathan-Turner had apparently been trying to contact the Bakers regarding the “future” segment, but they had only just returned from a lengthy holiday in Spain. Nathan-Turner explained the situation on the spot, and they agreed to meet with Saward immediately. The script editor was not enthusiastic about working with the Bakers again, but they had a reputation for writing quickly and so he proposed that they develop a mystery in space. The final episode should end with the Valeyard placing the Doctor in terrible danger, which Nathan-Turner thought might involve an accusation of genocide.

Over the weekend, the Bakers formulated a potential storyline. Taking up Saward's suggestion, they leaned on Agatha Christie's seminal 1934 novel Murder On The Orient Express, with a homicide taking place aboard a luxury transport -- in this case, the space liner Hyperion III. The story's monsters would be the Vervoids, a sentient form of vegetation which was inspired by research concerning a hormone shared by both plant and animal life. The name for these creatures came from the vervain, a genus of semi-woody flowering plants also known as the verbena. With the Bakers' quick work proving acceptable, their scripts were commissioned under the title “The Ultimate Foe” on March 13th.

Like Bidmead, the Bakers worked closely with Saward to try to avert any major problems, but communication became poor as he grew increasingly unhappy with the scripts. Finally, on April 2nd, Saward resigned from Doctor Who. His duties on the Bakers' episodes would be performed by Nathan-Turner; Saward would receive no televised credit on the broadcast programmes. The Bakers later referred to their adventure as “The Vervoids” but, in mid-April, Nathan-Turner decided that all fourteen episodes of Season Twenty-Three would be transmitted under the banner title The Trial Of A Time Lord. The “future” segment would consequently comprise Episodes Nine to Twelve. The title “Terror Of The Vervoids” would eventually become associated with the Bakers' scripts after they chose this name for their 1988 novelisation from Target Books.

Although the final six episodes of The Trial Of A Time Lord were essentially divided into two separate stories -- the Bakers' four scripts, plus the two-part conclusion, “Time Inc” -- it was decided that they would be grouped together as Serial 7C for production purposes. As such, they would largely share the same crew, including director Chris Clough, who had been recommended to Nathan-Turner by his partner, Gary Downie; Clough and Downie had worked together on EastEnders. Bonnie Langford had been cast as Melanie in late December, and she was delighted to learn that Clough had hired dancers to play the Vervoids to ensure that the creatures would move gracefully. Having appeared frequently on stage, Langford had worked with several of the Vervoid artistes before, and she was amused to see them made up as Doctor Who monsters.

Chris Clough decided to complete Episodes 13 and 14 before starting work on the Bakers' scripts

Production on Serial 7C began with location filming, which solely involved material for the concluding segment of The Trial Of A Time Lord. As such, once work moved to the studio, Clough decided to complete Episodes Thirteen and Fourteen before starting work on the Bakers' scripts. This meant that Lynda Bellingham (the Inquisitor) and Michael Jayston (the Valeyard) could wrap up their obligations to Doctor Who: the pair featured heavily in the trial's closing installments, but only in cut-ins from the Time Lord courtroom during Episodes Nine to Twelve. Consequently, these were the first sequences taped for the Vervoid adventure, in BBC Television Centre Studio 1 on July 16th.

The first studio block dedicated entirely to the Bakers' scripts took place in TC3 from July 30th to August 1st. On the initial day, Clough completed scenes in the gymnasium and started on those in the passenger cabins -- all of which were redressed versions of the same set -- and the bulkhead. This work continued on the middle day, when the TARDIS sequences were also taped. Clough then began recording material in the hydroponic centre, the work hut and the cargo hold, with the same settings required for the last day of the session. For the Episode Nine cliffhanger, Nathan-Turner asked Langford to scream in the key of F, since this would segue perfectly into the closing theme music.

Clough's team reassembled in TC3 from August 12th to 14th. The primary focus on the first two days was the Hyperion III lounge; in addition, the cabin set was redressed as Janet's compartment for the first day, while the second day saw cameras rolling on the bridge. A minor emergency occurred on the 12th when the tube through which Vervoid actor Peppi Borza was “exhaling” marsh gas accidentally dropped down inside his mask, threatening to choke him. Fortunately, the headpiece was removed before it was too late and, after being cleared by the medical staff, Borza was able to return to work. The last day of production on Season Twenty-Three then saw the completion of various corridor scenes, as well as those in the waste disposal unit, the communications room and the isolation cabin.

A sense of pessimism permeated the proceedings as recording drew to an end. Unusually, no confirmation had yet come from BBC brass that Doctor Who would be returning for its twenty-fourth season, igniting fears that the programme's final episodes might now be in the can. Exacerbating matters was the release of the September 1986 edition of the science-fiction magazine Starburst on August 13th. In a scathing and detailed interview, Saward gave his side of the story behind his departure from Doctor Who, reserving his harshest criticisms for Nathan-Turner. The press soon seized on the article: it was the first time that such behind-the-scenes dirty laundry had been aired so publicly. Even when the BBC finally announced Doctor Who's renewal on August 19th, Nathan-Turner was relieved by his certainty that the programme was continuing without him...

• Doctor Who Magazine #323, 13th November 2002, “Archive: The Trial Of A Time Lord Parts Nine To Twelve” by Andrew Pixley, Panini Publishing Ltd.
• Doctor Who Magazine Special Edition #3, 22nd January 2003, “It's Alright (Baby's Coming Back)” by Andrew Pixley, Panini Publishing Ltd.
• Doctor Who: The Complete History #42, 2017, “Story 143: The Trial Of A Time Lord”, 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 Sixth Doctor by David J Howe, Mark Stammers and Stephen James Walker (1993), Virgin Publishing.
• In·Vision #88, January 2000, “Production” edited by Anthony Brown, Cybermark Services.