At the Doctor's trial, the Valeyard presents the Doctor and Peri's most recent adventure. On the trail of arms merchants, they arrive on Thoros-Beta, home of the Mentors -- including their old foe, Sil. There they are attacked by a genetically-modified monster created by the scientist Crozier. He is searching for a way to save Kiv, the Mentor leader, whose enhanced intelligence is now causing his brain to outgrow his skull. Peri forges a reluctant alliance with a brash and headstrong warlord named King Yrcanos. But the Doctor is subjected to mind-altering technology... and appears to cast his lot with Crozier and the Mentors.

The villainous Sil, created by Philip Martin for 1985's Vengeance On Varos, had proved highly popular with Doctor Who producer John Nathan-Turner and script editor Eric Saward. Martin was quickly asked to bring the character back for a second encounter with the Doctor, and he began to develop “Mission To Magnus”, which paired Sil with the Ice Warriors. However, this adventure became a casualty of the BBC's decision to delay and shorten Season Twenty-Three. Instead, Martin was recruited to the team of writers assembled for the retooled version of the 1986 season, in which all of the scripts would be linked by the Doctor's trial at the hands of the Time Lords.

The new Season Twenty-Three was patterned after the 1846 Charles Dickens novel A Christmas Carol, with evidence at the trial given in the form of the Doctor's past, present and future adventures. Following a meeting on July 9th, Martin was tasked with devising the “present” segment -- that is, the Doctor's most recent exploits prior to his summons to the Time Lord courtroom. Once again, it was suggested that Sil should be incorporated into the storyline. Martin took the opportunity to further develop the capitalist critique which had been an element of Vengeance On Varos. In particular, he envisaged Thoros-Beta as being a world entirely devoid of natural resources, which had prompted the native Mentors to subsist by manipulating investments in the wider galaxy. Martin also wanted to address his concerns about the emerging science of genetic engineering.

Nicola Bryant was worried that her career might suffer from a prolonged association with a single role

Another requirement for Martin's narrative stemmed from discussions about the future of Peri Brown. Peri would have remained with the Doctor throughout the original Season Twenty-Three and, during a meeting in the summer of 1985, Nathan-Turner indicated to actress Nicola Bryant that this plan remained unchanged. However, Bryant was beginning to worry that her acting career might suffer from a prolonged association with a single role. She was also keen to leave Doctor Who in a memorable fashion, having felt that the exit of her predecessor, Janet Fielding, in 1984's Resurrection Of The Daleks was notably lacklustre. As such, Nathan-Turner and Bryant agreed that Peri would be killed off in the eighth episode of the season -- the concluding installment of Martin's serial.

Since writing Vengeance On Varos, Martin had joined BBC Radio as a drama producer; consequently, staff clearance was requested for Martin's Doctor Who scripts on September 13th, 1985. The title “The Planet Of Sil” was originally applied to the narrative, which soon became known as “Mindwarp”. During the writing process, Matrona Kana's name was modified slightly, becoming Kani; matrona was the Latin form of “matron”. Ron Jones was engaged as director, making what would prove to be his sixth and final Doctor Who serial. He had most recently handled Vengeance On Varos, and likely would have served in the same capacity on “Mission To Magnus”.

As “Mindwarp” neared production, Nathan-Turner decided that the entirety of Season Twenty-Three should be broadcast as a single, fourteen-part serial. Consequently, Martin's story would become Episodes Five to Eight of The Trial Of A Time Lord. Nabil Shaban agreed to reprise the role of Sil. He would wear the same body as had been constructed for Vengeance On Varos, but a new headpiece was fabricated which had more frills. Amongst the other castmembers assembled by Jones was Brian Blessed, an acclaimed Shakespearean actor who had risen to prominence on television in the police drama Z Cars. In August 1983, the British press had erroneously identified Blessed as the man who would succeed Peter Davison as the star of Doctor Who.

Martin was surprised and dismayed by some of the changes Saward made to his “Mindwarp” scripts. He had tried to adhere to the instructions of Michael Grade, the Controller of Programmes for BBC One, to emphasise humour over violence, only to discover that Saward had eliminated many of the comedic elements he had developed. “Mindwarp” would turn out to be his final contribution to televised Doctor Who. For his part, Colin Baker was mystified by the Doctor's aberrant behaviour, and he asked Saward to explain whether this was meant to be a ruse, a genuine reflection of the effects of Crozier's machine, or evidence of tampering with the Matrix record. Saward, however, offered no clarification; soon thereafter, on April 2nd, he resigned as Doctor Who's script editor.

For her death scene, Nicola Bryant used her natural British accent, as opposed to Peri's American twang

Studio work for the second segment of The Trial Of A Time Lord took place in two three-day sessions. The initial block spanned May 27th to 29th at BBC Television Centre Studio 1 in White City, London. The first two days concentrated on scenes in Crozier's laboratory, with work in the corridors also starting on the second day. Unfortunately, painstaking lighting changes provoked a labour dispute and, as a result, the work proceeded slowly. On the last day, Jones was only able to complete material in Kiv's chamber and profit room, alongside additional corridor sequences; this represented significantly less than what he had planned to accomplish. For Peri's death scene, Bryant wore a bald skullcap, although she had to be careful to keep her head still in order to maintain the illusion. Bryant also used her natural British accent -- as opposed to the American twang she normally adopted for Peri -- which was then modulated in the same manner as the Mentor version of Kiv. Meanwhile, to save money, the Possican delegate was represented by a repainted Terileptil mask, originally constructed for 1982's The Visitation.

The second studio block ran from June 11th to 13th in TC6, with tunnel scenes on Jones' agenda throughout. Also recorded on the first day was material in Matrona Kani's chamber, the tidal control room and the cell. Jones' schedule for the second day, which included sequences in the Alphan induction centre and the cavern, provoked a flare-up of the industrial strife which had plagued the earlier session. For the induction centre, designer Andrew Howe-Davies intended to lower two of the studio lighting rigs to serve as circular entranceways, but the lighting crew objected to the use of their equipment for this purpose. Fortunately, a compromise was brokered whereby Howe-Davies abandoned his plan to use the actual lights on the rigs, and work was soon progressing so smoothly that Jones was able to make up for the earlier delays.

However, another problem arose on the last studio day, during which all of the courtroom scenes would be recorded. When Jones' team arrived at TC6, they discovered that the set had not been erected -- almost duplicating the error that had plagued the first segment of The Trial Of A Time Lord a month earlier. This time, fortunately, the scenery crew managed to correct the mistake quickly enough that Jones was able to complete all of the required shots.

Production then wrapped up with location filming on June 15th and 16th at Peacehaven in East Sussex, where the Telscombe Cliffs were the venue for sequences on the pebble beach and at the Rock of Sorrows. Unfortunately, on the 16th, it was discovered that a crewmember had accidentally noted the times of high and low tide in reverse. As a result, the water became much deeper than anticipated as the day progressed, and Bryant grew particularly concerned about the battery pack powering her microphone when shooting the scene of the Doctor and Peri arriving on Thoros-Beta. Jones worked quickly to complete this material before the actors' safety was comprised. In post-production, a new digital compositor called HARRY was used to alter the colours in these scenes. The lurid result was in accordance with Martin's scripts, which described Thoros-Beta as boasting purple mountains, a bright green sky and a pink sea.

June 16th was Bryant's last day on Doctor Who, and a farewell party was held that night at Nathan-Turner's home in nearby Brighton. During the festivities, the producer acknowledged that the concluding installment of The Trial Of A Time Lord would explain that Peri had not died on Thoros-Beta after all. Bryant was disappointed that this revelation would undermine such a powerful and unusual exit from Doctor Who. News of her forthcoming departure reached the British press on July 20th.

• Doctor Who Magazine #249, 12th March 1997, “Archive: The Trial Of A Time Lord Parts Five To Eight” by Andrew Pixley, Marvel Comics UK 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 #87, November 1999, “Production” edited by Anthony Brown, Cybermark Services.