The four companions find themselves in eighteenth-century France, during the dying days of Robespierre's blood-drenched Reign of Terror. Ian, Barbara and Susan are captured by soldiers of the Revolutionary Army and thrown into a grubby prison run by an enigmatic governor named Lemaitre. The women are sentenced to death at the guillotine, while a dying spy entrusts Ian with a vital message. Meanwhile, the Doctor poses as a member of the new ruling elite and embarks on a mission to save his friends. But in a land of suspicion where hidden agendas abound, can anyone be trusted to help?

In late February 1964, Doctor Who story editor David Whitaker planned to write an adventure entitled “The New Armada”, set in sixteenth-century Spain, for the tail end of the programme's first recording block. However, it appears that Whitaker soon changed his mind and began searching for a replacement. On March 10th, Whitaker met with Dennis Spooner at the recommendation of Dalek creator Terry Nation, who was a colleague of Spooner's at Associated London Scripts. Spooner already had some science-fiction experience on the Gerry Anderson puppet series Fireball XL5 and Stingray, and so was rather dismayed when Whitaker indicated that he was seeking an historical serial. Nonetheless, Spooner agreed to research several potential settings suggested by Whitaker and develop a proposal.

About a week later, Spooner informed Whitaker that his preferred historical era was the French Revolution, which had originally been proposed to the story editor by William Russell. This was a period during the French Revolution of 1789 to 1799 when the state was effectively controlled by the Committee of Public Safety, led by Maximilien Robespierre. Thousands were executed during la Terreur: not only those who supported the French aristocracy, but also many who were in favour of a republican France but who argued that the Committee's powers were either too extensive or too limited. The Reign of Terror culminated in late July 1794, when divisions in the French government resulted in the arrest and execution of Robespierre and several of his closest allies. These climactic events would lie at the heart of the narrative.

The material involving the mysterious English spy James Stirling was inspired by The Scarlet Pimpernel

Spooner's serial was commissioned on April 2nd, as The Reign Of Terror. He was asked to craft his scripts in a manner that would ensure that William Russell could appear only in pre-filmed material for the second and third episodes. Russell could thus become the last of the regular castmembers to enjoy a two-week holiday. The material involving the mysterious English spy James Stirling was inspired by Baroness Orczy's 1905 novel The Scarlet Pimpernel (derived from a 1903 play), itself set during the Reign of Terror. A minor name change saw Leon Corneille become Leon Colbert.

For a time, it was expected that The Reign Of Terror would be the first serial of Doctor Who's second season, with a six-week hiatus following the broadcast of The Sensorites. In late May, however, the Controller of Programmes for BBC One, Donald Baverstock, decided that the break in transmission should occur later than originally planned. Consequently, The Reign Of Terror became the last story of Doctor Who's first season, with Planet Of Giants now leading off its second year.

The Reign Of Terror was written during a period when Doctor Who's future was deeply uncertain. This was primarily because of the unsuitability of its regular studio space, Lime Grove Studio D in Shepherd's Bush, London. A suggested alternative was Lime Grove Studio G -- with Studios 3 and 4 at BBC Television Centre in White City, London being made available when possible -- but this was a very long, narrow facility unsuited to the large sets often employed in the series. Finally, in June, it was agreed that Doctor Who would be shifted to Riverside Studio 1 in Hammersmith, London toward the end of the recording block. In the interim, it appears that The Reign Of Terror was written with Studio G's unusual dimensions in mind. The first four episodes would be taped there, with parts five and six shifting to TC4.

When “The New Armada” was still being planned, the intended director was Gerald Blake (who would eventually make The Abominable Snowmen and The Invasion Of Time). In the event, Hungarian emigre Henric Hirsch received the assignment for The Reign Of Terror. Hirsch had only recently completed the BBC's directors' training course, but his work on an episode of First Night had been noticed by Doctor Who producer Verity Lambert.

Production on The Reign Of Terror began on June 15th, when Doctor Who enjoyed a small amount of location filming for the first time. This took place on the grounds of White Plains, a nursing home in Denham, Buckinghamshire, and on the Isle of Wight Farm at nearby Gerrards Cross. It was limited to three shots of the Doctor walking to Paris in part two, Guests Of Madame Guillotine. In this instance, Brian Proudfoot doubled for William Hartnell to avoid having to disrupt rehearsals for The Sensorites. Proudfoot had attended the recording of that serial's third episode on June 12th to study Hartnell's mannerisms and walk.

From June 16th to 18th, filming took place at the BBC Television Film Studios in Ealing, London. Amongst the sequences recorded were model shots of the farmhouse, as well as William Russell's material for episodes two and three. Jeffry Wickham, playing Webster, recorded all of his scenes up to Webster's death on the first morning. Assuming Hirsch had no further need of him, he left to meet a friend for lunch and drinks, only to learn that he still had to play Webster's corpse during the afternoon. Under the influence of the alcohol he had consumed, Wickham fell asleep during the filming, and woke after several hours... to find the studio deserted.

Studio recording then began with part one, A Land Of Fear, on July 10th. As had been typical throughout the season, each episode of The Reign Of Terror was then taped on successive Fridays. Unfortunately, it was already clear to many castmembers that Hirsch was struggling. The pace of production on Doctor Who was more gruelling than on the handful of programmes he had directed to date, and Hirsch -- whose background was in the theatre -- was not particularly interested in the material. He also had difficulty forging a good working relationship with the actors, and especially with William Hartnell, who was often intolerant of foreigners and could be impatient with inexperienced directors.

Hirsch's difficulties escalated on July 24th when part three, A Change Of Identity, was recorded. Scenes involving a horse and cart were particularly challenging to camera rehearse, and Hirsch started to complain of feeling unwell. During a break in rehearsals that afternoon, production secretary Ann Earl and production assistant Timothy Combe (later a Doctor Who director on The Silurians and The Mind Of Evil) discovered that Hirsch had collapsed just outside the production gallery.

With Hirsch obviously unable to continue, Lambert was summoned; she and Combe oversaw the remainder of the day's rehearsals. It appears that John Gorrie -- who had previously worked on The Keys Of Marinus -- was urgently summoned to handle that evening's recording, although Gorrie himself has no recollection of these events. Fortunately, Hirsch was well enough to resume his duties for the remaining three installments of The Reign Of Terror. To alleviate some of the pressure, it was agreed that Combe would assume a portion of the director's responsibilities. Combe was also able to convince Hartnell to soften his attitude towards Hirsch.

Major changes to Doctor Who were contemplated, including writing out Barbara and replacing Susan

Meanwhile, it was during the production of The Reign Of Terror that major decisions about Doctor Who's long-term future were being made. Only two more serials -- Planet Of Giants and The Dalek Invasion Of Earth -- were left to be recorded as part of the first production block; these would be held over to start the programme's second season in October. Lambert and Whitaker had been contemplating major changes to the regular cast beyond this point, including writing out Barbara (although this idea was later dropped) and replacing Susan with a different teenaged girl. However, manoeuvres such as these would be pointless if there was no guarantee that Doctor Who would continue on for any significant length of time.

Since the end of May, Donald Baverstock had been unwilling to commit to more than a single additional serial, to keep Doctor Who on the air until late January 1965. By the end of July, the only significant decision he had made was to increase the break in transmission after The Reign Of Terror to seven weeks. This meant that, were Doctor Who to end in January, a four-part serial would have to be hastily commissioned to fill out the run, since none was currently in development. Furthermore, Lambert feared that it would be difficult to convince her regular cast to agree to such a brief contract extension. Indeed, she was worried that even if a decision to prolong Doctor Who was eventually made, it might come too late: Hartnell had already received another job offer, and Russell's agent was actively seeking other opportunities for his client.

Finally, on August 14th -- the same day that production wrapped on The Reign Of Terror -- Baverstock informed Lambert that he was renewing Doctor Who for thirteen more weeks, with the possibility of a further thirteen episodes beyond that. A month later, the broadcast of Prisoners Of Conciergerie on September 12th brought Doctor Who's first season to a close. It was a year which had already seen new ground broken for British television. But no one could suspect at the time that it was merely the beginning...

• Doctor Who Magazine #204, 29th September 1993, “Archive: The Reign Of Terror” by Andrew Pixley, Marvel Comics UK Ltd.
• Doctor Who Magazine Special Edition #7, 12th May 2004, “Do You Want To Know A Secret?” by Andrew Pixley, Panini Publishing Ltd.
• Doctor Who: The Complete History #3, 2016, “Story 8: The Reign Of Terror”, edited by Mark Wright, Hachette Partworks Ltd.
• Doctor Who: The Handbook: The First Doctor by David J Howe, Mark Stammers and Stephen James Walker (1994), Virgin Publishing.
• Doctor Who: The Sixties by David J Howe, Mark Stammers and Stephen James Walker (1992), Virgin Publishing.