The Doctor, Leela and K·9 find themselves aboard the R1C, a spacecraft from the doomed Minyan civilisation, which destroyed itself using technology given to them by early Time Lords. For a hundred thousand years, Jackson and his three-person crew have been searching for the P7E, the ship carrying the Minyan race banks, with which they hope to revive their people. The Doctor helps them trace the P7E to a spiral nebula, where space debris has formed a planet around it. But, on penetrating to the planet's core, they discover a downtrodden people -- the Trogs -- who suffer under the rule of the unseen Oracle.

Anthony Read was hired to replace Robert Holmes as Doctor Who's script editor in May 1977. With Holmes planning to formally vacate the position in July, it was agreed that Read would be given full control over Season Fifteen's final two serials. He was soon discussing ideas for the season finale with David Weir but, because Weir was a newcomer to Doctor Who, Read quickly realised that he would need considerable attention. As such, he was eager to put the year's penultimate adventure in reliable, experienced hands. Holmes recommended the writing team of Bob Baker and Dave Martin, Doctor Who veterans who had already contributed The Invisible Enemy to the season. Indeed, Holmes had previously discussed further scripts with Baker and Martin.

During his time as script editor, Holmes had enjoyed considerable success by plumbing classic literature to inspire ideas for Doctor Who, and Read now thought along similar lines. He suggested that Baker and Martin look to Greek mythology, and the three men soon focussed on the legend of the Argo -- the ship which bore Jason and other Greek heroes, the Argonauts, on a quest to find the fabled Golden Fleece. The tale, told in Apollonius' third-century BC Argonautica and in other ancient works, seemed ripe for transposing onto a science-fiction setting. The resulting scripts, called Underworld, were commissioned on June 23rd.

Many of the character names were variations on the legendary Argonauts

Far from masking their source material, Baker and Martin made numerous references to it. Many of their character names were variations on the legendary Argonauts: Commander Jackson was named for Jason himself (and this was explicitly acknowledged in dialogue from the closing scene), Herrick for the strongman Heracles (better known to modern audiences by his Roman name, Hercules), Orfe for the minstrel Orpheus, and Tala for the huntress Atalanta. Idas and Idmon shared their names with two minor Argonauts, while Naia was a reference to the water nymphs known as Naiads. The Minyans of legend were actually the ancient Greek race from whom many of the Argonauts were supposed to have been descended. The Trogs were a reference to the Troglodytes, a cave-dwelling people in ancient Greek texts. The name for the Oracle itself was borrowed from a number of Greek prophetesses, often associated with the god Apollo, the most famous being the Oracle at Delphi.

In the legend, the Argo was Jason's boat; the spaceship R1C, originally simply referred to as the R1, was meant to recall it. (Its name may also have been derived from the common misconception that the stories of Jason and the Argonauts are collectively known as the Argosy, in the same way that the tales of Odysseus are called the Odyssey.) Similarly, the P7E was named for the deity Persephone. This held two meanings: Persephone was a fertility goddess -- hence the P7E carrying the Minyan race banks -- and she came to be imprisoned in the Underworld. Indeed, the Greeks also referred to the Underworld as Hades and, at one point, Baker and Martin considered referring to the realm of the Trogs as Hadis.

Several incidents in the story of Jason and the Argonauts provided plot points for Underworld. The Episode One cliffhanger in which the R1C was pummelled by asteroids referenced Jason's encounter with the Symplegades, also called the Clashing (or Cyanean) Rocks. These were large boulders situated along the Bosphorus which haphazardly smashed into one another, destroying any ship which was caught in-between. The grove on the island of Colchis in which the Golden Fleece hung was guarded by serpents, and this was the inspiration for the P7E's defence system.

Greek mythology was not Baker and Martin's only inspiration. The notion of the Minyan race banks came from an article in Scientific American about genetics. Ankh was named for an Egyptian symbol for life, while Lakh came from an Indian word for “one hundred thousand”, referring to the timespan of the Minyans' search for the P7E. Relatively modern figures provided names for the guards. Rasmus Rask was a Danish philologist whose pioneering research in the early nineteenth century demonstrated links between various ancient languages, including Greek. In the early twentieth century, the French poet Pauline Tarn -- who wrote under the nom de plume Renée Vivien -- was a noted translator of the works of the classical Greek poet Sappho. Austrian painter Gustav Klimt, who worked from the late nineteenth century, featured ancient Greek subjects on several occasions. Another artist of the early twentieth century, Max Liebermann of Germany, lent his name to the Liebemann maser weapons.

Bob Baker and Dave Martin were asked to provide a strong role for K·9

Baker and Martin also drew upon their own recent Doctor Who scripts by giving the Minyans a signature motto: “The Quest is the Quest”. This followed in the tradition of their previous catchphrases, “Eldrad must live” (from 1976's The Hand Of Fear) and “Contact has been made” (from The Invisible Enemy). Furthermore, Read asked Baker and Martin to provide a strong role for K·9, whom they had created for The Invisible Enemy.

To direct Underworld, Williams requested the services of Norman Stewart. Stewart was usually a production assistant -- including on several Doctor Who serials, most recently The Invisible Enemy -- but he occasionally worked as a director as well. Williams advised Stewart that he was concerned about the fact that Underworld would be broadcast around the start of 1978, since this would coincide with the UK release of Star Wars, which was already a monster hit in North America. Williams knew that Doctor Who's usual production standards would compare poorly with George Lucas' pioneering film. To enhance the serial's visual appeal, Williams and Stewart decided to abandon plans to pre-film some of the subterranean sequences at the BBC Television Film Studio, and instead invest the majority of the Underworld budget into two impressive sets: the R1C (which could be redressed as the P7E) and the caverns.

In late summer, Williams went on holiday for two weeks. When he returned, he found the end of Season Fifteen in complete disarray. Not only did it appear that Weir had badly misjudged what was possible on a Doctor Who budget, rendering his finale -- “Killers Of The Dark” -- unusable, but skyrocketing inflation had resulted in the estimates for the Underworld sets coming in at three times the anticipated budget. One of Williams' directives upon taking over Doctor Who had been to cut down on overspending. As such, he was left with only two options: either truncate the season so that it ended with Underworld, or else find a novel and money-saving approach to the serial's production.

At this stage, work had already begun on the elaborate set for the R1C. Williams' solution, then, was to abandon the proposed cavern set and instead represent the subterranean environment with cost-effective models, onto which the cast could be superimposed using the chroma key effects technique. Stewart already had some experience with this method, having seen it utilised -- albeit to a much more limited extent -- on The Invisible Enemy. After further investigation, he and designer Dick Coles determined that the approach was feasible, despite the fact that such extensive chroma key work had never before been attempted in a BBC production.

The cast and crew found the effects-dependent recording method to be extremely frustrating

As work started on Underworld, the cast was rejoined by John Leeson, who had been contracted on September 7th to provide the voice of K·9 in the adventure. Leeson had been absent from the previous serial in production, Image Of The Fendahl, during which K·9 appeared only fleetingly. Underworld was made at BBC Television Centre Studio 3 in White City, London, beginning with two days of chroma key recording on October 3rd and 4th. It was hoped that this time would be sufficient to complete all of the serial's cavern sequences, but this proved impossible despite substantial overruns. The cast and crew found the effects-dependent recording method to be extremely frustrating and nerve-wracking, and Tom Baker's mood became notably sour. His ongoing displeasure with the Leela character was particularly evident, further straining his relationship with Louise Jameson.

Indeed, it was around this time that Jameson confirmed to Williams that she was not interested in returning to Doctor Who for Season Sixteen. The producer was very disappointed; he liked Leela and harboured some hope that he might be able to change Jameson's mind. Nonetheless, Williams got in touch with Elisabeth Sladen to see if she would be interested in returning to Doctor Who as Sarah Jane Smith, whom she had played for three years until 1976's The Hand Of Fear. Sladen was unavailable, however, and so work began on a brand new character.

Williams decided that the new companion should draw a stark contrast with Leela. As such, he developed the idea of the Doctor being assigned a novice Time Lord by a higher power (a Guardian of Time, who figured prominently in Williams' plans for the next season). This would be the brilliant but sheltered Romy -- short for Romanadvoratrelundar -- who would be intellectual and reserved where Leela had been savage and emotive. A character outline for Romy was distributed on October 10th.

Unusually, the second studio block for Underworld was four days long -- spanning October 15th to 18th -- in order to provide time for the remaining chroma key shots. Work on the 15th involved scenes on the R1C for Episode One, as well as all of the material aboard the TARDIS. Imogen Bickford-Smith suffered a severe allergic reaction to the combination of cotton wool and latex paint which was applied to give Tala the appearance of advanced old age, and a physician had to be summoned to treat her symptoms. The R1C sequences from Episodes Two to Four were completed on the 16th. These sets were then redressed to pose as the P7E for recording on the 17th. It was Jameson's turn to experience some medical distress, when she developed throat pain after breathing in the dry ice which represented the fumigation gas. Finally, the remaining cavern scenes -- mostly from the latter half of the serial -- were completed on the 18th. Some model shots were also recorded on this day, although others were captured on film at Bray Studios in Water Oakley, Berkshire. They were effectively the last remnants of Williams' plan to give Underworld a Star Wars-scale aesthetic.

The substitution of chroma key effects for traditional sets was not as successful as anticipated

Beginning with Invasion Of The Dinosaurs in 1973, Doctor Who had occasionally been allocated a “gallery-only” day for post-production. Ever since taking over as producer, however, Williams had been campaigning to have a gallery-only day built into the production schedule for every Doctor Who serial. In light of the volume of work which confronted electronic effects supervisor AJ “Mitch” Mitchell on Underworld, Williams' lobbying finally bore fruit, and a gallery-only day was scheduled for October 21st. Despite this, however, the substitution of chroma key effects for traditional sets was not as successful as the production team had anticipated, leading to a great deal of disappointment with the finished serial.

On November 7th, the BBC confirmed that Jameson would be leaving Doctor Who at the end of the season. In a bid to gain extra exposure for her client, Bickford-Smith's agent soon began publicly touting Tala as Leela's replacement. Press articles suggesting that Bickford-Smith would be the new companion began appearing on November 13th -- even though the production team had never considered this as an option.

It was originally intended that Underworld Episode One would air on December 24th, one week after the conclusion of the previous serial, The Sun Makers. In the event, however, Doctor Who took a two-week break during the holidays, and Underworld began its broadcast on January 7th, 1978. With The Basil Brush Show and Bruce Forsyth And The Generation Game -- the programmes which had previously bookended Doctor Who -- having wrapped up their seasons, a revamped BBC Saturday evening line-up greeted the new year. Doctor Who now aired twenty minutes later, at 6.25pm. It was preceded by Jim'll Fix It and followed by Saturday Night At The Movies.

Despite the production problems which had plagued Underworld, Baker and Martin remained enthusiastic about the scenario they had created. For a time, they considered spinning off the R1C crew into their own science-fiction programme, in which the Minyans would travel through space and become involved in new adventures based upon other tales drawn from ancient mythology. Ultimately, however, nothing would come of this idea.

• Doctor Who Magazine #243, 25th September 1996, “Archive: Underworld” by Andrew Pixley, Marvel Comics UK Ltd.
• Doctor Who Magazine Special Edition #8, 1st September 2004, “Nobody Does It Better” by Andrew Pixley, Panini Publishing Ltd.
• Doctor Who: The Complete History #28, 2017, “Story 96: Underworld”, edited by John Ainsworth, Hachette Partworks Ltd.
• Doctor Who: The Handbook: The Fourth Doctor by David J Howe, Mark Stammers and Stephen James Walker (1992), Virgin Publishing.
• Doctor Who: The Seventies by David J Howe, Mark Stammers and Stephen James Walker (1994), Virgin Publishing.
• In·Vision #28, November 1990, “Production” edited by Justin Richards and Peter Anghelides, Cybermark Services.