Under the failing influence of the White Guardian, the TARDIS materialises aboard a spacecraft disguised as an Edwardian racing yacht. Its captain, Striker, is competing in a race across the solar system. He and his officers are Eternals -- immortal beings incapable of creative thought -- while the sailors are “ephemerals”, mortals whose minds give the Eternals sustenance. Tegan attracts the interest of the first mate, Marriner, while the Doctor suspects that one of the Eternals is cheating to win the mysterious prize of Enlightenment. Meanwhile, Turlough begins to realise that there may be no escape from the Black Guardian...

Prior to becoming the script editor of Doctor Who, Eric Saward had largely worked in radio, where he came to know writer Barbara Clegg. Clegg was a regular viewer of Doctor Who, which she watched with her children. In 1981, she and Saward began discussing ideas for the programme, and Clegg took inspiration from her extended family, which spanned several social strata. In particular, the way that her wealthier relations interacted with their poorer kin reminded Clegg of gods toying with lesser mortals, which led to the notion of the Eternals. The concept of solar winds -- actually streams of charged particles ejected from the Sun -- prompted the image of sailing ships racing through space. For the prize of such a competition, Clegg developed Enlightenment from the Tree of the Knowledge of Good and Evil, as described in the Book Of Genesis.

The confluence of these ideas appealed to Saward and producer John Nathan-Turner, who appreciated their originality. On September 22nd, they commissioned Clegg to write a storyline called “The Enlighteners”. It was envisaged as the concluding serial of a three-story arc involving the Black and White Guardians, and so Clegg duly wrote these characters into her narrative, replacing the Enlighteners who originally awarded the race's prize. The script for Episode One was then requested on October 22nd, followed by the remaining three installments on January 5th, 1982.

Barbara Clegg gave the Eternals names with nautical connotations

As she developed her scripts for “The Enlighteners”, Clegg gave many of the Eternals names with nautical connotations. Aboard the Shadow, Captain Striker's surname came from a steamboating term for an engineer's apprentice, while Marriner was a slight corruption of “mariner”. Captain Wrack of the Buccaneer took her surname from an archaic word for a shipwreck. Critas the Greek was inspired by Critias, one of the dialogues of the philosopher Plato which told the story of the lost city of Atlantis. Captain Davey was an allusion to the phrase “Davy Jones' locker”, meaning the depths of the ocean.

By late April, concern was growing that the trilogy's first adventure -- Pat Mills' “The Song Of The Space Whale” -- would not be ready for its scheduled production dates in late August. It was briefly thought that “The Enlighteners” might be brought forward to take its place in the recording order, where it would be directed by Peter Moffatt. Instead, Saward was able to commission Peter Grimwade at short notice to fill the void with Mawdryn Undead. As such, “The Enlighteners” was restored to its original place in the schedule, to be both made and broadcast fifth in Doctor Who's twentieth season.

In September, Saward amended the title to Enlightenment, which he felt was more enigmatic. By this point, Fiona Cumming had been assigned to direct Clegg's serial; she had recently completed work on Snakedance, the first story of the current production block. It was Cumming's idea that the Eternals would not blink, and she strove to find actors who could adopt a suitably aloof demeanour. Also in the Enlightenment cast was Valentine Dyall, making his final appearance as the Black Guardian. He was joined by Cyril Luckham, reprising the role of the White Guardian he had originally played in 1978's The Ribos Operation.

Production on Enlightenment began with three days at the BBC Television Film Studios in Ealing, London. Spanning November 3rd to 5th, the schedule involved material on the decks of the Shadow and the Buccaneer, as well as in space. Unfortunately, the shot of Turlough jumping overboard did not go as planned: the harness supporting Mark Strickson malfunctioned, leaving him walking with discomfort for several weeks. Model filming then took place at Ealing from November 8th to 12th. The 8th was also the day that Peter Davison was contracted for all twenty-six episodes of Season Twenty-One. However, Davison was now considering leaving Doctor Who, and so no option was included for the following year.

With the electricians on strike, it appeared that Enlightenment might have to be abandoned

During the autumn of 1982, the BBC was labouring under the threat of industrial action by the electricians' union. This had resulted in Terminus, the story made immediately before Enlightenment, losing one of its studio days, and it was becoming clear that subsequent serials were in even greater peril. Enlightenment was scheduled to be made in two blocks, the first to take place on November 16th and 17th, and the second running from November 30th to December 2nd. Unfortunately, in early November, the electricians did indeed go on strike. All of Cumming's studio days were postponed, and it appeared that Enlightenment -- along with the final two stories of Season Twenty, The King's Demons and “The Return” -- might have to be abandoned.

Happily, the strike was resolved in late November. To avoid having to extend contracts on multiple serials, it was decided that The King's Demons would be recorded in December as scheduled. This left Nathan-Turner with the difficult decision of what to do with Enlightenment. Since it was narratively crucial -- resolving the Black Guardian trilogy and establishing Turlough's permanent place in the TARDIS -- the producer decided that it would have to be made on the studio dates originally allocated to “The Return”, which would be dropped from the run. As a result, The King's Demons would now serve as the season finale. All was not lost for “The Return”, however: a revised version would eventually air in 1984 as Resurrection Of The Daleks.

With the recording of Enlightenment having been postponed for two months, Cumming took the opportunity to enjoy a vacation in Lanzarote, in Spain's Canary Islands. Upon her return, she found herself having to make several crew changes, and replace two actors who were now unavailable. Peter Sallis and David Rhule had originally been cast as Striker and Mansell, respectively, but the roles would now be played by Keith Barron and Leee John. John was the lead singer of pop band Imagination, whose hit Just An Illusion had peaked at number two in the British charts in March 1981. Cumming herself had to relinquish an assignment on the soap opera Take The High Road in order to complete Enlightenment.

Meanwhile, Nathan-Turner was confronted with discontent from his regular cast. Davison, Strickson and Janet Fielding all disliked the dynamic that had developed between the Doctor, Turlough and Tegan; Davison wondered why the Doctor would choose to travel with such seemingly disagreeable companions. Nathan-Turner accepted their criticism, and encouraged them to work together to improve their characters' rapport. Around the same time, visual effects designer Mike Kelt approached the producer about the dilapidated state of the TARDIS console. Nathan-Turner informed Kelt that there was no money to refurbish or redesign the prop for Enlightenment, but he indicated that he would address the designer's concerns as soon as possible.

Tegan's sumptuous ball gown proved challenging for Janet Fielding to wear, given its plunging neckline

Under its revised schedule, both studio blocks for Enlightenment would take place at BBC Television Centre Studio 1 in White City, London. The first session finally went ahead on January 17th and 18th, 1983. The initial day concentrated on scenes in the TARDIS, before work began on material set aboard the Buccaneer. The remainder of the sequences on Wrack's vessel were then planned for the following day. Tegan's sumptuous ball gown proved challenging for Fielding to wear, given its plunging neckline. At one point, Davison concluded a line with the ad-lib, “Oh, and Tegan, put your boobs back in!” whereupon Fielding realised that she had accidentally exposed herself.

On January 25th, Saward asked Clegg to provide an additional ninety seconds of content for Episode One, and a further two minutes for Episode Two. Clegg delivered these pages on the 30th, adding dialogue between the sailors and Turlough about the America, as well as Jackson's attempted rebellion. The second studio block then took place from January 30th to February 1st, and largely dealt with scenes on the Shadow. On the middle day, Cumming also had to record some material in the Buccaneer grid room and its adjoining passageway, which she had been unable to finish on the 18th. The belated completion of Enlightenment brought Doctor Who's twentieth production block to an end. However, Davison, Fielding and Strickson would soon be reunited for the Doctor Who twentieth-anniversary special, The Five Doctors, which went before the cameras in March.

Meanwhile, Davison advised Nathan-Turner that Season Twenty-One would indeed be his last. He had been unimpressed with the writing on Season Twenty, and was dismayed by the lack of budget and resources afforded Doctor Who by the BBC. In addition, Davison was mindful of the counsel of Patrick Troughton, who had played the Second Doctor, to remain in the role no longer than three years. Soon thereafter, Fielding and Strickson also confirmed that they wanted to leave Doctor Who during the following season. It was rapidly becoming clear that 1984 would see Doctor Who completely reinvented once again...

• Doctor Who Magazine #186, 13th May 1992, “Archive: Enlightenment” by Andrew Pixley, Marvel Comics 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 127: Enlightenment”, 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 #67, September 1996, “Production” edited by Anthony Brown, Cybermark Services.