The Doctor experiences regenerative instability, prompting him to live as a hermit amidst the desolation of Titan 3. There he rescues Lieutenant Hugo Lang, the lone survivor of a pursuit squadron destroyed by the immense power of the tyrannical Mestor. The Doctor learns that Lang was trying to rescue twin mathematical geniuses named Romulus and Remus Sylvest, and he recognises their kidnapper as his old friend, the Time Lord Azmael, whom he thought retired to the planet Joconda. The Doctor must discover the link between Mestor and Azmael, and the terrible purpose Mestor intends for the Sylvest twins.

Part of the motivation behind casting Colin Baker as the Sixth Doctor was to create as great a contrast with Peter Davison, the outgoing star of Doctor Who, as Davison had made with his own predecessor, Tom Baker. Over the summer of 1983, the primary concern of producer John Nathan-Turner and script editor Eric Saward -- not to mention Baker himself -- was the development of the new Doctor. It was agreed that Baker should adopt many of his own larger-than-life characteristics, diverging from the more subdued demeanour of Davison's incarnation. It was also felt that Baker should emphasise the Doctor's alien origins, exhibiting thought processes that were not always of a human nature.

The Sixth Doctor would therefore be unpredictable, argumentative and boisterous, sometimes offering a worldview very much at odds with his companion's; he would solve problems with dizzying leaps of logic in the manner of Sherlock Holmes. Baker wanted to make viewers initially suspicious of his Doctor, but gradually earn their trust over the course of his tenure. Nathan-Turner aspired to craft a character similar to the remote but ultimately reliable Mr Darcy in Jane Austen's 1813 novel Pride And Prejudice. It was also thought that the new Doctor should boast very florid dialogue, spouting a plethora of quotations -- both real and fictional -- and demonstrating a penchant for obscure vernacular. Baker hoped that children would be encouraged to look up the unusual words in a dictionary, thereby helping to expand their vocabularies.

Colin Baker would have a full serial of his own at the end of Season 21

It was suggested that these defining mannerisms should be accentuated in the Sixth Doctor's debut serial, with his regeneration provoking manic and violent mood swings. Again, this was meant to provide a contrast with the Fifth Doctor, whose own introductory story -- 1982's Castrovalva -- had seen him amnesiac and vulnerable. It was acknowledged that great skill was needed to tackle such a challenging writing assignment, especially since Nathan-Turner and Saward had made the unusual decision to give Baker a full serial of his own at the end of Season Twenty-One, before the break in transmission. The portrayal of the Sixth Doctor in this adventure, then, would be the abiding impression in viewers' minds for nine months.

To this end, Nathan-Turner suggested recruiting veteran writer Anthony Steven, with whom he had worked on All Creatures Great And Small. Saward agreed to approach the writer, although he and Nathan-Turner had very different impressions of the kind of narrative they should pursue. Nathan-Turner wanted a straightforward adventure pitting the Doctor against a strong villain, while Saward felt that the new Doctor's personality would be better showcased in a more unusual storyline. This was just one of an increasing number of points of disagreement between the producer and his script editor. Indeed, although Saward liked Baker personally, he had significant misgivings as to whether the actor was the right choice to play the Doctor.

On July 19th, Steven submitted a storyline entitled “A Stitch In Time”. He was asked to script Episode One on August 2nd; the title had now been amended to “A Switch In Time”. The remaining installments were commissioned on August 24th, by which time the title had changed again, to The Twin Dilemma. The character of Azmael was inserted into the narrative at the prompting of unofficial fan adviser Ian Levine, who had proposed an encounter between the Doctor and the old mentor described in 1972's The Time Monster and 1980's State Of Decay. Unfortunately, Steven misunderstood the nature of the Doctor's relationship with the character, and made Azmael a tutor at the Prydonian Academy instead. Meanwhile, the tense rapport between the Doctor and Peri was encouraged by Nathan-Turner, who erroneously believed that the newly-regenerated Doctor typically quarrelled with his companions. For his part, Saward was growing concerned that Peri was not a good match for Baker's vision of the Doctor.

Anthony Steven began explaining his slow progress with increasingly bizarre excuses

During the autumn, Steven's progress on The Twin Dilemma slowed to a crawl. To the mystification of the production team, he began explaining away his problems with increasingly bizarre excuses -- most famously, a claim that his typewriter had “literally exploded”! To make matters worse, The Twin Dilemma did not meet the approval of its assigned director, Peter Moffatt, who had most recently worked on the twentieth-anniversary special The Five Doctors. Moffatt implored Saward to intervene, pointing out a number of issues of both storytelling and logistics. By now, however, Steven had fallen badly ill, and could not continue working on the serial. In fact, The Twin Dilemma would be his final television credit before his death in 1990.

Left with no other choice, Saward took on the task of overhauling The Twin Dilemma himself. He restructured the climax of the adventure, shifting it from outer space back to Joconda, and beefed up Mestor's role. He also excised the suggestion that Mestor was in fact possessed by an extraterrestrial intelligence called Aslan or Azlan. The Chamberlain was originally female, while Commander Fabian -- apparently an homage to the Fifties crime drama Fabian Of Scotland Yard -- was male, and merely a general. Azmael, meanwhile, took his name from Azazel, a fallen angel described in the Book Of Enoch. Remus and Romulus Sylvest were named after the legendary founders of Rome.

While the scripts for The Twin Dilemma were slowly hammered into shape, other elements of Doctor Who's new era were falling into place. Having been contracted for the final five episodes of Season Twenty-One on September 30th, Baker's services for Season Twenty-Two were secured on October 4th. This contract also included an option for three additional years: Nathan-Turner was keen to avoid the brevity of Davison's tenure, while Baker -- long an enthusiastic fan of Doctor Who -- was in fact eager to eclipse Tom Baker's record of seven seasons as the Doctor.

The accord between the new star and his producer did not extend to the Sixth Doctor's costume. Baker preferred a black velvet outfit, but Nathan-Turner vetoed this on the grounds that it was too similar to the Master's usual apparel. Instead, the producer wanted something totally tasteless to replace Davison's understated cricketing garb, and costume designer Pat Godfrey had to go back to the drawing board several times before finally achieving a look which Nathan-Turner found sufficiently garish. Godfrey was instructed to omit the colour blue from her pallet to avoid interfering with chroma key effects shots, and was asked to retain the question mark collars that Nathan-Turner had introduced in 1980. Baker's addition to the ensemble was a cat badge, which he would often swap out. Its inclusion was inspired by The Cat That Walked By Himself, a tale from Rudyard Kipling's 1902 anthology Just So Stories. Baker was otherwise reluctant to embrace Nathan-Turner's preferred design; indeed, years later, the producer himself admitted that the costume had been a mistake, and worked against the show.

John Nathan-Turner was forced to reallocate the first studio block for The Twin Dilemma to The Caves Of Androzani

Disaster nearly struck The Twin Dilemma in late November, when a strike by the BBC's scenery shifters crippled Davison's farewell adventure, The Caves Of Androzani. One of the serial's two studio sessions was lost as a result, leaving Nathan-Turner no choice but to reallocate the first studio block for The Twin Dilemma, from January 10th to 12th, 1984, to the Fifth Doctor's swansong. One year earlier, a similar set of circumstances had resulted in the loss of the Season Twenty finale (which was eventually made as Resurrection Of The Daleks for Season Twenty-One). Fortunately, The Twin Dilemma would have a different fate: Nathan-Turner successfully persuaded his superiors to allocate a new studio session to the serial, given its importance as Baker's debut.

As production neared, Moffatt found himself bedevilled by the search for identical twin teenaged boys to play Remus and Romulus Sylvest. At one point, Moffatt believed that he had located twin girls who would be suitable, but Nathan-Turner was opposed to the change of gender. At the last minute, Moffatt was approached by an agent representing Andrew and Paul Conrad -- the latter going by the stage name “Gavin” to avoid confusion with another actor named Paul Conrad. Moffatt was unimpressed by the boys' acting ability and lack of experience, but he reluctantly agreed to hire them all the same. Their father, Les Conrad, had been an extra on Doctor Who on several occasions, and was given the non-speaking role of a Jocondan guard so that he could serve as the boys' chaperone.

During rehearsals for The Twin Dilemma, Baker was dealing with a personal tragedy: his seven-week-old son, Jack, had become a victim of cot death in late November. Baker also got off on the wrong foot with his co-star, Nicola Bryant. Having only started on Doctor Who in October, Bryant felt uncomfortable welcoming Baker to the cast as if she were a well-established veteran. Baker, however, thought that Bryant was being aloof, and set about trying to win her over. At one point, he even bit the actress on her posterior, later admitting that this had been entirely inappropriate. Bryant finally invited Baker to lunch, where they had the opportunity to develop a better mutual understanding. The two actors would soon develop a strong camaraderie.

Recording for The Twin Dilemma finally began with what should have been its second three-day block, from January 24th to 26th at BBC Television Centre Studio 8 in White City, London. The first two days dealt with scenes in the TARDIS and the Titan 3 safe house. Also recorded on the initial day was material aboard “Edgeworth's” spacecraft, during which Colin Baker provided the voice of Joconda Control, while the set for the ducting was in use on the middle day. On the last day of the block, Moffatt tackled more scenes on the spaceship, as well as those in the Sylvest twins' playroom and the ops room.

The changes to the production schedule meant that, unusually, location filming for The Twin Dilemma took place between the two studio sessions. On February 7th, CJ Wren & Sons' Springwell Quarry in Rickmansworth, Hertfordshire posed as the surface of Titan 3. The next day, exterior scenes on Joconda were shot in Gerrards Cross, Buckinghamshire at the Wapseys Wood quarry owned by the Gerrards Cross Sand & Ballast Company.

The rescheduled studio session for The Twin Dilemma was then held from February 14th to 16th in TC3. Throughout the block, taping took place on the sets for Mestor's throne room and various corridors, while Azmael's lab was also needed on the first two days. The TARDIS console room was once again required for the final day of recording, which drew the production of Season Twenty-One to a close.

There was still work to be done before the new Doctor could make his televised debut, however, including revisions to the title sequence. Sid Sutton, who had introduced the starfield-style graphics for Tom Baker's final season in 1980, worked with Terry Handley to add a rainbow effect which was meant to complement the Sixth Doctor's colourful personality. At Nathan-Turner's suggestion, Sutton incorporated two images of Baker to make the new Doctor appear to smile when his face appeared. The neon Doctor Who logo was also updated, with the colour changed and its flat shape slightly distorted.

It was this amended title sequence which greeted viewers when Episode One aired on March 22nd. Although sports-related programming had followed the Friday Doctor Who broadcasts throughout most of the season, the BBC now scheduled movies to air after The Twin Dilemma. This was how Season Twenty-One came to an end on March 30th; the transmission of Episode Four also closed the door on the three-year experiment of scheduling Doctor Who twice weekly. The next programme to regularly occupy the Thursday timeslot was the quiz show Pot The Question, while Fridays saw Doctor Who replaced by the animated The Pink Panther Show.

• Doctor Who Magazine #270, 21st October 1998, “Archive: The Twin Dilemma” by Andrew Pixley, Marvel Comics UK Ltd.
• Doctor Who Magazine Special Edition #3, 22nd January 2003, “Doctor! Doctor!” by Andrew Pixley, Panini Publishing Ltd.
• Doctor Who: The Complete History #40, 2015, “Story 136: The Twin Dilemma”, 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 Sixth Doctor by David J Howe, Mark Stammers and Stephen James Walker (1993), Virgin Publishing.
• In·Vision #77, April 1998, “Production” edited by Anthony Brown, Cybermark Services.