Many years ago, the people of the planet Marinus developed the Conscience, a computer with the power to control minds. It was used only to keep the peace until Yartek, leader of the evil Voords, overcame its influence. To prevent Yartek from using the Conscience as a weapon, the five keys that power it were hidden. Now the scientist Arbitan believes he can defeat Yartek and compels the Doctor, Susan, Ian and Barbara to embark on a quest to recover the keys. But many dangers lie between the companions and their goal: hypnotic monsters, killer plants, ice zombies, and finally a charge of murder.

By the end of September 1963, much of Doctor Who's first season had started to take shape. It would begin with Anthony Coburn's 100,000 BC, Terry Nation's The Daleks and John Lucarotti's Marco Polo. These would be followed by an untitled “miniscules” story from Robert Gould, Coburn's “The Masters Of Luxor”, an historical adventure from Malcolm Hulke known as “Britain 408 AD”, a seven-part serial with an unspecified historical setting to be provided by story editor David Whitaker, and Nation's 1857-set “The Red Fort”. In October, Whitaker's brief Inside The Spaceship was inserted between The Daleks and Marco Polo, and more science-fiction was incorporated when “Britain 408 AD” was replaced with a different Hulke narrative, “The Hidden Planet”.

By the dawn of 1964, however, unresolved problems with both Gould's and Coburn's serials meant that “The Hidden Planet” would now be transmitted fifth, immediately after Marco Polo. Unfortunately, as Hulke began delivering his scripts, it became clear to the Doctor Who production team that the serial required considerable work. With less than two months left before recording was due to begin, this meant that a replacement adventure would have to be commissioned very quickly.

Terry Nation would hastily write a science-fiction story to replace “The Hidden Planet”

Nation, meanwhile, had not particularly enjoyed writing for Doctor Who and it appears that he did little work on “The Red Fort”. But when The Daleks began airing at the end of December, the title monsters were instantly popular and the programme's ratings skyrocketed. As such, on January 21st, Nation met with Whitaker and producer Verity Lambert to discuss additional scripts for Doctor Who. They agreed that “The Red Fort” should be abandoned; in its place, Nation would hastily write a six-part science-fiction story to replace “The Hidden Planet”, having demonstrated an ability to write quickly on The Daleks. Because the serial would have to be completed in just four weeks, Whitaker offered to help Nation with ideas, and it was suggested that the story should be made up of several small adventures to expedite the process.

Nation's serial soon became known as The Keys Of Marinus. Only some of the background details he developed survived into the televised version. As Nation conceived it, the Voord were alien invaders who took advantage of the vulnerable state into which the people of Marinus had been rendered by the pacifying effects of the Conscience. The Conscience was deactivated so that the Voord could be opposed. Eventually, however, the Voord's protracted stay on Marinus meant that they, too, became susceptible to the machine. Arbitan (whose name was meant to evoke “arbiter”) therefore despatched agents to recover the keys which would reactivate the Conscience, so that the invaders could finally be defeated.

The opening and closing episodes were devised by Nation alone. The second and fifth installments arose from discussions between Nation and Whitaker. Whitaker came up with the idea of a house full of traps for part three; Nation transferred this notion to an exterior setting because the first two episodes had largely taken place indoors. It was Whitaker who suggested a nordic environment for part four, to contrast with the jungle setting of the previous installment.

Amongst later changes made to Nation's scripts was the removal of a TARDIS sequence from episode one, The Sea Of Death. Here it was revealed that the reason for the Doctor's foul mood when he first appeared in the programme's initial serial, 100,000 BC, was because he had sought the help of the BBC in restoring colour to the TARDIS scanner screen -- only to find them “infernally secretive”!

The director assigned to The Keys Of Marinus was John Gorrie, who had been promoted from assistant floor manager around the start of 1963. Gorrie was very reluctant to work on Doctor Who, having aspired to direct classics and lacking interest in science-fiction. Work began with filming on March 5th, at the BBC Television Film Studios in Ealing, London. This included the first-ever shot of the TARDIS materialising, a model effect of the Ship landing on the beach.

With William Hartnell allocated a holiday, David Whitaker restructured episodes three and four to eliminate the Doctor

Meanwhile, it had been decided that the four regular characters were now sufficiently well-established that the principal castmembers could each be given two-week breaks, spread out over the remainder of the season. First to be allocated a holiday was William Hartnell and so, on March 17th, Whitaker restructured the third and fourth episodes of The Keys Of Marinus to eliminate the Doctor entirely. Originally, he accompanied Susan and Sabetha in The Snows Of Terror, and his ring would have been found in Vasor's hut along with the travel dials and Conscience keys. Instead, he would now leap ahead to Millenius, the location of the final key. Rather than appearing only in the second episode, Altos was written into the rest of the serial to compensate for the Doctor's absence.

Recording for The Sea Of Death took place on Friday, March 20th, at Lime Grove Studio D in Shepherd's Bush, London; as usual, the remaining five episodes were taped on consecutive Fridays. Hartnell was absent on both April 3rd and 10th while he enjoyed his vacation.

On March 26th, Whitaker was forced to defend the third installment, The Screaming Jungle, against a charge of plagiarism levied by Robert Gould. On February 4th, Whitaker and Gould had agreed that his “miniscules” adventure would be abandoned due to insurmountable difficulties with the scripts. Gould had suggested that he might instead write a story about a planet where plants treat people the way that the people on Earth treat plants. On February 9th, Gould informed Whitaker that he had decided against developing the concept. Now, however, he was concerned that The Screaming Jungle -- with its hostile plant life -- had been inspired by his idea. Whitaker was able to satisfy Head of Serials Donald Wilson that this was not the case.

On April 25th, The Screaming Jungle became the first episode of Doctor Who to be broadcast under the BBC One channel name; BBC Television had rebranded itself in conjunction with the debut of BBC Two on April 21st. With the broadcast of episode five, Sentence Of Death, Doctor Who reverted back to its original 5.15pm timeslot after just six weeks at 5.30pm. The programmes adjacent to it in the schedule, The Telegoons and Juke Box Jury, were likewise now starting a quarter of an hour earlier.

The rights to Nation's first three Doctor Who serials -- The Daleks, The Keys Of Marinus and The Dalek Invasion Of Earth -- were all optioned by Amicus for adaptation as feature films. But while the other two adventures eventually made their way to the big screen, the rights to The Keys Of Marinus were eventually dropped. This was likely due to the absence of the Daleks from the story.

• Doctor Who Magazine #310, 14th November 2001, “Archive: The Keys Of Marinus” by Andrew Pixley, Panini Publishing 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 #2, 2016, “Story 5: The Keys Of Marinus”, edited by John Ainsworth, Hachette Partworks Ltd.
• The Doctor Who Production Diary: The Hartnell Years by David Brunt (2024), Telos Publishing 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.