In the thirty-eighth century, the Le Verrier space station is a scientific facility in orbit around Neptune. When it goes silent, a rescue team led by Commander Nagata is despatched, and encounters the Doctor and Clara. Soon they are attacked by creatures made up of particulate matter, which Clara dubs Sandmen. They discover that Le Verrier is where Gagan Rassmussen has been conducting experiments to improve his Morpheus pods: devices which compress a full night's sleep into a matter of minutes. The Doctor realises that the Sandmen are the children of the Morpheus process -- and represent a threat to all humanity.

By 2010, Mark Gatiss had already written several Doctor Who stories, and was exploring potential ideas for a new submission. Steven Moffat had recently become the programme's executive producer, and he had demonstrated a keen ability to turn the mundane -- like statues and dust captured in sunbeams -- into the stuff of nightmares. Suffering from insomnia one night, Gatiss' thoughts turned to the rheum made of mucus and skin cells that often formed near a person's eyes as they slept. This “sleep” was often said to be left by the Sandman, a character in European folklore who induced slumber with a sprinkle of magical dust. Gatiss pondered whether it presented an opportunity to follow Moffat's example, by turning such a common phenomenon into the basis for a Doctor Who adventure.

With this notion as his starting point, Gatiss began developing a two-part story in which the “Wideys” or “Wide Awakes” used a machine to drastically abbreviate their need to sleep. They were pitted against the “Rips”, named after the title character of Washington Irving's 1819 short story Rip Van Winkle, who fell asleep for twenty years after meeting a group of strange men in the mountains near his home. Gatiss intended the adventure to be a satire on capitalism and the constant creep of work responsibilities into an employee's every waking hour. For younger viewers, he imagined that the machine would cause the Wideys' rheum to evolve into monstrous Sandmen. However, Gatiss struggled to make the narrative work, and he eventually moved on to other concepts.

Mark Gatiss was advised that his story structure was too similar to Under The Lake / Before The Flood

Several years later, Gatiss turned his attention to a new Doctor Who script after completing Robot Of Sherwood for Season Thirty-Four. Moffat had allowed for the possibility that Gatiss' next contribution might be deferred to the following year, and the writer saw this as an opportunity to resurrect the Sandman concept. Moffat was planning to feature a number of two-part adventures in Season Thirty-Five, and Gatiss proposed that a suitable approach to his storyline would be for the first episode to examine the aftermath of the Sandmen's creation, after which the Doctor and Clara would travel back in time to witness their origins in the second installment. However, Moffat advised Gatiss that this structure would be too similar to Toby Whithouse's Under The Lake / Before The Flood, which was also being developed for Season Thirty-Five.

Searching for a new angle on the material, Gatiss observed that Doctor Who had not yet pursued a “found footage” format, of the type popularised by the 1999 horror film The Blair Witch Project, which was meant to be assembled from video footage shot by missing students as they explored a purportedly-haunted forest. Gatiss thought that an unexpected twist would be the revelation that the cameras which appeared to be recording the events of the Doctor Who story would turn out to be something more sinister. He realised that this could be another manifestation of the corrupted rheum at the heart of the Sandman story, and suggested merging the two concepts. Moffat was enthusiastic, and he agreed with Gatiss that such an adventure would work best if it were limited to a single episode. Gatiss wanted events to culminate in just a partial victory for the Doctor; Moffat appreciated the opportunity to show that the Doctor was not infallible. This approach would also provide Gatiss with a set-up for a potential sequel, in which he could return to the more satirical narrative he had originally envisaged.

For his first Doctor Who script set in the future -- after seven which took place in the past or the modern day -- Gatiss was keen to paint a society which would be distinctly different from that of contemporary Earth. Having recently taken trips to Japan and India, he imagined the product of both cultures blending together over the course of centuries. Gagan Rassmussen, the villain of the piece, was crafted with actor Reece Shearsmith in mind. The two men had worked together for many years as part of the League of Gentlemen comedy troupe, and they shared a lifelong love of Doctor Who. Indeed, Shearsmith had previously enjoyed a cameo appearance as Patrick Troughton, the actor who had played the Second Doctor, in Gatiss' 2013 docudrama An Adventure In Space And Time.

The Sandmen were originally able to take the form of carnivorous dust clouds

In the script's original draft, Rassmussen used the alias “Bell” during his initial interactions with the time travellers and the rescue team, only acknowledging his true identity when he revealed himself to be alive at the adventure's climax. The Sandmen were also able to take the form of carnivorous dust clouds. Their victims were kept in a state of near-death, cocooned in webs on the station's ceiling, and it was their perspective that provided much of the story's footage. Amongst the rescue team, 474 was originally called Babu. During early 2015, Gatiss gave his script the title Sleep No More. As cited by the Doctor, this was a reference to William Shakespeare's 1606 play Macbeth: the eponymous character claimed to hear these words spoken after murdering King Duncan, indicating the toll that the gravity of his deed was beginning to take upon his conscience.

Having been positioned as the ninth episode in the Season Thirty-Five broadcast schedule, Sleep No More was initially paired with episode ten, Face The Raven, to form the year's fifth production block under director Justin Molotnikov. In late April, however, it was decided that the two stories would be split up, with Sleep No More initially remaining as Block Five. By mid-May, however, it was agreed that Face The Raven would take its place, and Gatiss' script was instead deferred to Block Seven. Molotnikov would continue to serve as its director. This meant that Sleep No More would see Jenna Coleman's return to Doctor Who after almost a month off, during which Peter Capaldi had recorded Block Six -- Heaven Sent -- in which he effectively carried the action on his own.

Amongst Molotnikov's cast was Bethany Black, playing 474. A longtime fan of Doctor Who, Black was a stand-up comedian who had recently moved into television with roles in Cucumber and Banana, created by former Doctor Who executive producer Russell T Davies. Her casting in Sleep No More marked the first time that an openly transgender individual had appeared in the programme. Meanwhile, during the episode's readthrough on July 23rd, producer Nikki Wilson agreed to voice the lines assigned to the Le Verrier computer. Having been an actress early in her career, Wilson was delighted with the experience and, since nobody had yet been cast in the role, it was agreed that she would also provide the dialogue, uncredited, in the finished episode.

Production on Sleep No More began on July 27th and 28th at Roath Lock Studios in Cardiff, for scenes in the Le Verrier corridors. Molotnikov's team then spent the 29th to the 31st on the premises of G24 Power, a solar cell manufacturer in Newport. First up was material in the Morpheus lab, which occupied the initial day and part of the middle day. Attention then turned to sequences in the kitchen, with this work continuing to the last day at G24. Cast and crew then returned to Roath Lock, where a fire alarm interrupted Molotnikov's plan to continue with corridor footage. Nonetheless, Rassmussen's cut-ins to the audience were taped that evening, prior to a break for the weekend.

August 3rd and 4th were spent at Roath Lock, with cameras rolling on the set for the rescue ship's crew room; sequences in the cargo bay were also taped on the first day, and Molotnikov completed some of the postponed corridor shots on the second day. On the 5th, the Fillcare manufacturing plant in Pontyclun offered spaces suitable for the engine room and the chamber in which the TARDIS materialised. The main venue on August 6th and 7th was Wild Water Cold Storage, on the Queen Alexandra Docks in Cardiff. A working walk-in freezer at the location was used for the scenes of the Doctor, Clara and Nakata eluding the Sandmen, with breaks scheduled after each take to ensure that no one suffered unduly from the frigid environment. The afternoon of the 7th then saw more hallway material completed at Roath Lock, alongside several inserts.

Three more studio days were scheduled after the weekend, from August 10th to 12th, focussing on sequences which required only the rescue team, many of which took place in the Le Verrier corridors. On the first day, Molotnikov also completed work in the crew room and the cargo bay, along with green screen shots of the Morpheus presenter and the singers. The latter were intended to evoke the Chordettes, the American quartet who rose to fame with their 1954 rendition of Mr Sandman. Deep-Ando's demise on the viewing platform was on the itinerary for the second day, while various pick-up shots were recorded on the last day.

To emphasise the “found footage” nature of the episode, it was agreed that the regular Doctor Who title sequence would be abandoned for Sleep No More. Instead, a brief animated graphic was shown which mixed names relevant to the story with random characters; highlighted letters spelled the words “Doctor Who” in a vertical orientation. As a result, the episode title did not appear until the start of the closing credits. When Sleep No More aired on November 14th, Doctor Who returned to its 8.15pm timeslot and once again led into Casualty, which had been postponed the week before.

• Doctor Who: The Complete History #83, 2018, “Story 259: Sleep No More”, edited by John Ainsworth, Hachette Partworks Ltd.