While the Doctor relaxes, Romana finds the fourth segment of the Key To Time on the planet Tara. She is then kidnapped by the villainous Count Grendel, who has mistaken her for an android duplicate of Princess Strella, whom he also holds prisoner. Grendel has aspirations to the Taran throne, to which Strella is second in line. He plans to undermine the claim of the heir apparent, Prince Reynart, then marry Strella. But with the princess unwilling to cooperate, Grendel now intends to compel Romana to take her place. Meanwhile, the Doctor allies himself with Reynart in a desperate attempt to stop Grendel's bid for power.

With the overarching storyline of the search for the Key To Time running throughout Doctor Who's sixteenth season, many details had to be nailed down at an early stage. Indeed, by January 1978, five of the six adventures had already been decided. The first four would be The Ribos Operation by Robert Holmes, The Pirate Planet by Douglas Adams, The Stones Of Blood by David Fisher and “Shield Of Zarak” by Ted Lewis, while the concluding serial would be Bob Baker and Dave Martin's The Armageddon Factor. This left only the fifth slot to be determined.

Script editor Anthony Read had been very pleased with Fisher's work on The Stones Of Blood, and quickly decided to offer him the season's remaining adventure. At about the same time, Lewis' battles with his personal demons resulted in the abandonment of “Shield Of Zarak”. One possible hook for Lewis' narrative had been the Doctor's discovery that the historical Robin Hood was actually a villain. Read asked Fisher to come up with a storyline in the same swashbuckling mould, and suggested a Doctor Who version of The Prisoner Of Zenda. In Anthony Hope's 1894 novel, Rudolf Rassendyll saved the kingdom of Ruritania from the machinations of the evil Duke Michael by taking the place of the kidnapped King Rudolf V, who was both his namesake and his doppelganger. “The Androids Of Zenda” was duly commissioned from Fisher on May 26th.

Michael Hayes became apprehensive of The Power Of Kroll's ambitious technical requirements

The same day, Robert Holmes was contracted to write The Power Of Kroll, which was intended to replace “Shield Of Zarak” as the season's fourth story. Since Holmes was a Doctor Who veteran -- and Read's predecessor as script editor -- it was felt that he would be able to put together a workable adventure in short order. By now, Michael Hayes had been assigned to direct The Power Of Kroll, marking his first work on Doctor Who. Unfortunately, as Holmes' scripts began arriving in mid-June, Hayes became very apprehensive of its ambitious technical requirements.

Meanwhile, Fisher was also making steady progress on his serial, which was now called “The Prisoners Of Zend”. Other titles apparently under consideration had included “The Androids Of Zend”, “The Prisoner Of Zend” and “The Seeds Of Time”; the latter was part of a short-lived effort to unify the titles of all of the Key To Time stories under the format “The [Something] Of Time”. To allay Hayes' concerns, producer Graham Williams agreed to interchange “The Prisoners Of Zend” and The Power Of Kroll in both the production and broadcast schedules; Hayes was much more comfortable with the content of Fisher's adventure.

In constructing his scripts, Fisher broadly followed Hope's outline for The Prisoner Of Zenda, and included many analogous characters. King Rudolf became Prince Reynart (so called after Renart the fox, the French folkloric character popularised in Pierre de Saint Cloud's twelfth-century novel Le roman de Renart), Antoinette de Maubin became Madame Lamia (named for a female demon in Greek mythology), Sapt became Zapp and then Zadek, Fritz von Tarlenheim became Farrah, and Princess Flavia became Princess Strella. Duke Michael and his henchman, Rupert of Hentzau, were combined into Count Grendel (whose name was drawn from the antagonist of the epic Old English poem Beowulf). Fisher was very proud of this character in particular, and decided to have Grendel escape the events of “The Prisoners Of Zend” in the hope that he might return in a future serial. The role of Rudolf Rassendyll was essentially shared by the Doctor and the android “George”. The Archimandrite's title, meanwhile, was actually that of a senior abbot in orthodox Christian churches.

Fisher's scripts were originally set on the planet Zend, with the site of the coronation being a castle located in Tara. This was a reference to the ancestral seat of the kings of Ireland -- and, according to mythology, of the supernatural Tuatha dé Danann. Fisher had hoped that Zend might be populated by animals resembling creatures of legend such as unicorns -- either natural or mechanical -- and originally envisaged Till as a dwarf rather than a hunchback. However, Williams indicated that the more fantastical elements should be dropped for budgetary reasons, along with overt references to Hope's novel. As such, Tara became the name of the planet, and the serial was duly retitled The Androids Of Tara.

Fisher had constructed his scripts so that Castle Gracht could be realised in the studio, but Hayes was able to secure permission to film in and around Leeds Castle in Leeds, Kent. This was the site of a fortification dating from the early twelfth century, although the modern edifice was largely the result of nineteenth-century construction. It offered venues suitable for both Castle Gracht and the Taran countryside.

One of the scenes scheduled for the first day at Leeds -- July 24th -- was of the Doctor fishing. Tom Baker was given an antique fishing rod to use... which he inadvertently tossed into the River Len during rehearsals. Stunt arranger Terry Walsh had to dive in and rescue it. Later the same day, it was Hayes' teenaged son, Patrick, who made the bushes rustle to signify the approach of the Taran Beast. Her budget taxed, costume designer Doreen James was only able to construct a headpiece for the Beast, barely concealing the fact that it was worn over a rented bear costume. James was more satisfied with the eclectic outfit she designed for Romana, which boasted Mary Tamm's favourite colours: purple and turquoise.

On July 25th and 26th, Leeds Castle was open to the public during the day, so recording was largely nocturnal. With the same constraint in place on the 27th, Hayes instead concentrated on material outside the Pavilion of the Summer Winds, which was constructed for The Androids Of Tara in an isolated part of the castle grounds. The venue was closed to the public again on July 28th, providing Hayes with greater freedom to shoot around Leeds Castle itself. On this day, another water-related mishap occurred when the sound recordist fell into the moat while the scenes of K·9 in the boat were being filmed.

Because so much material had been filmed on location, studio recording for The Androids Of Tara was divided into a pair of two-day sessions; originally, it was expected that the second block would be three days long. The first of these took place on August 14th and 15th at BBC Television Centre Studio 6 in White City, London. Scenes recorded on the first day included those in the TARDIS, the android surgery, Strella's room in the palace, and Strella's cell. The second day dealt with some of the material in and around the dungeon -- particularly Prince Reynart's cell -- plus the coronation room and its antechamber.

With August 27th having been dropped from the shooting schedule, the second studio block encompassed only August 28th and 29th; the venue was now TC1. The dungeon sequences were completed on the first day, leaving action in the hunting lodge, the great hall, the tunnel and the Pavilion of the Summer Winds to the final day. Unusually, the opening credits for The Androids Of Tara were recorded such that the episode number appeared prior to the writer's name, rather than the other way round.

• Doctor Who Magazine #293, 26th July 2000, “Archive: The Androids Of Tara” by Andrew Pixley, Panini Publishing Ltd.
• Doctor Who Magazine Special Edition #9, 22nd December 2004, “I'll Put You Together Again” by Andrew Pixley, Panini Publishing Ltd.
• Doctor Who: The Complete History #29, 2017, “Story 101: The Androids Of Tara”, 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 #35, December 1991, “Production” edited by Justin Richards and Peter Anghelides, Cybermark Services.