In Turmezistan, the sudden appearance of an ancient pyramid in close proximity to the Earth's three mightiest armies heralds the start of the Monks' scheme to take over the planet. Once again pressed into service as President of the world, the Doctor finds himself coordinating the responses of the American, Russian and Chinese forces, even as the Monks promise that the end of the human race is at hand. Meanwhile, a series of seemingly random events, playing out in a Yorkshire agricultural research lab, holds the key to the Monks' insidious plan...

Peter Harness' second Doctor Who story was Season Thirty-Five's The Zygon Invasion / The Zygon Inversion. Shortly after its production concluded in June 2015, businessman and television personality Donald Trump made his controversial entry into the race to become president of the United States. Trump's combative rhetoric often stoked the fires of intolerance, but his ability to confidently promote simple fixes for complex problems -- even if they were unlikely to be sustainable in the long term -- was attracting growing support. This prompted Harness to consider an alien equivalent to Trump, in order to explore the circumstances under which the people of Earth would willing cede their autonomy to an invading force. Faced with a crisis of global proportions, humanity would encounter beings who presented a benign facade and offered an easy solution, with the price being the world's independence.

Harness wanted the imminent global catastrophe to be man-made, but apolitical in nature. He recalled the efforts by a biotechnology company in the early Nineties to find a way to dispose of crop residue without burning, by genetically modifying a type of soil bacteria called Raoultella planticola. The engineered strain was subsequently assessed by microbiologist Elaine Ingham of Oregon State University, who warned that the company's failure to test their product in non-sterile soil had inadvertently led to the development of aggressive bacteria that had the potential to eradicate plant life worldwide. This doomsday scenario entered into popular culture, although Ingham subsequently acknowledged that her concerns were exaggerated. Harness decided to draw upon the mythology surrounding Raoultella planticola, dubbing the new strain DN8; this was a reference to the lethal insecticide DN6 in 1964's Planet Of Giants. The company manufacturing DN8 would be Global Chemicals, the same firm responsible for the oversized maggots of 1973's The Green Death.

Steven Moffat thought that the “kung fu Monks” were effective enough to appear across multiple linked episodes

For his villains, Harness conceived an alien race which lived outside time and space. They could use their study of parallel universes to understand the chains of probability that might rapidly lead to an extinction-level event. They would take the form of mummified corpses wearing robes; Harness imagined that they would also be skilled in hand-to-hand combat using martial arts, although this element would ultimately be dropped. Executive producer Steven Moffat saw a lot of potential in the “kung fu Monks”, and he thought that they were effective enough to appear across multiple linked episodes during Season Thirty-Six.

Harness' storyline was one of the first to be developed for Season Thirty-Six. It would feature a prominent role for new companion Bill Potts, who would ultimately be the person who acquiesced to the Monks. Writing began in early 2016, although adjustments had to be made during the summer to incorporate Nardole, who was originally absent from the narrative, as well as the story arc of the Doctor's blindness which would be introduced in episode five, Oxygen, and would now be the impetus for Bill's decision. Moffat would introduce the Monks in episode six, Extremis, with Harness' adventure positioned as episode seven. The final defeat of the Monks would be chronicled in episode eight, Toby Whithouse's The Lie Of The Land.

A first draft, entitled “First Contact (Number 122)” was completed around the middle of September. It featured Kate Stewart of the Unified Intelligence Taskforce (UNIT), and the title referred to the number of occasions on which the organisation had encountered alien lifeforms -- ostensibly, always for the first time. Kate alerted the Doctor to a situation in Morocco where a number of children were being influenced to collect bricks to build a pyramid. Once the last brick was in place, all the timepieces on Earth began to mirror the Doomsday Clock. One of the youngsters, Hassan, continued to serve as the Monks' mouthpiece. A brief visit via the TARDIS to a devastated 2018 confirmed the imminent annihilation that confronted humanity.

The Global Chemicals research facility was located in Idaho, and Erica worked for them as a truck driver. Apart from Douglas' hangover inducing him to misplace a decimal point, the other inciting incident was Erica dropping and breaking her smartphone when she was startled by her daughter, Em. As a result, after Erica collected a shipment of the lethal DN8, she was the only driver who couldn't be reached. Likewise, when the Doctor finally tracked her down as she was about to deploy DN8 in a wheatfield, Erica couldn't deactivate her dispersal unit because the necessary code was stored on her phone. As a result, the Doctor brought the unit to a sealed lab, inside which he became trapped due to his blindness.

Jemma Redgrave would be unavailable to play Kate Stewart, due to her commitments to Holby City

By mid-October, the Doctor Who production office had learned that Jemma Redgrave would be unavailable to play Kate Stewart, due to her commitments to the medical drama Holby City. Instead, the second draft replaced her with UNIT's Captain Walsh, the character played by Rebecca Front in The Zygon Invasion. The Global Chemicals facility was relocated to Yorkshire, and Erica was now a researcher there; instead of her phone, her glasses were broken by her daughter, Livvie. Hassan was the only juvenile possessed by the Monks, and the pyramid rose from the sand when he entered the exclusion zone between the American, Russian and Chinese forces. The 2018 sequence became a projection created by the Monks.

By early November, Moffat was still working on Extremis. As such, he and Harness would normally have coordinated to determine what changes needed to be made to “First Contact (Number 122)” to ensure that the two scripts were properly aligned. However, it was around this time that Moffat's mother fell gravely ill, leaving him with no opportunity to liaise with Harness. Instead, Moffat was forced to make the necessary revisions to “First Contact (Number 122)” himself, often doing so while sitting at his mother's hospital bedside. Sadly, Noreen Moffat would pass away during the Christmas period.

Moffat renamed the episode The Pyramid At The End Of The World. Hassan was omitted, Erica's glasses were broken by her husband rather than her daughter, and Captain Walsh was replaced with the Secretary General of the United Nations. The pyramid was now located in Turmezistan, the fictional country introduced in The Zygon Invasion. At a late stage, Global Chemicals became Agrofuel Research Operations to avoid confusion with an actual Global Chemicals. The Pyramid At The End Of The World joined Extremis as Block Five of the Season Thirty-Six production schedule. Daniel Nettheim, who had worked on The Zygon Invasion / The Zygon Inversion, returned to direct the two episodes.

Recording for The Pyramid At The End Of The World began on November 28th, the start of a week which saw Peter Capaldi absent while he worked on the family film Paddington 2. Consequently, the first day focussed on Bill and Penny's date in the student bar, a set at Roath Lock Studios in Cardiff which was normally used for the medical drama Casualty. As usual, Bill's flat was part of the Roath Lock backlot for the Welsh-language soap opera Pobol y Cwm. This was where work began on the 29th, before the intervening sequence of the couple walking home was shot along West Bute Street in Cardiff.

The Secretary General's death was a late addition; originally, he encouraged Bill to flee before she capitulated to the Monks

After a day off on Wednesday the 30th, a busy December 1st took in a number of Swansea locations. Erica's home was on Baldwins Crescent, her workplace was actually the Pilot Chemical Laboratory on Swansea University's Bay Campus, and Bill's journey in the Secretary General's vehicle was captured on nearby roads. Cast and crew then returned to the Pilot Chemical Laboratory on the 2nd, prior to a weekend off. Only at this stage was the name of the American bomber pilot changed from Pychoviack to Jackson. The death of the Secretary General was also a late addition; originally, he encouraged Bill to flee before she capitulated to the Monks. Capaldi rejoined Doctor Who for additional work at the Pilot Chemical Laboratory on December 5th and 6th, after which Nettheim spent the rest of the week filming material for Extremis.

For The Zygon Invasion, scenes in Turmezistan had been recorded in Fuerteventura, one of Spain's Canary Islands, off the coast of Morocco. A different part of the archipelago, Tenerife, would represent the country in The Pyramid At The End Of The World; it had previously hosted filming for the Season Thirty-Five premiere, The Magician's Apprentice / The Witch's Familiar. Essential cast and crew flew to Tenerife on December 11th, with cameras rolling there from the 12th to the 15th. The venue was the Hospital Militar de Abades, a facility near the village of Abades which was originally constructed in the middle of the twentieth century to treat Tenerife's leprosy epidemic. This was the last work on the episode prior to the Christmas break.

When production on The Pyramid At The End Of The World resumed in 2017, it was almost entirely confined to Roath Lock. The first set in use was for the eponymous pyramid itself, with recording spanning January 4th to 6th. Part of the latter day was also spent in the United Nations base, with Nettheim completing this footage on the 7th. After a day off on Sunday the 8th, January 9th saw recording aboard the Doctor's presidential aeroplane. The material in the Secretary General's vehicle was then remounted on the Roath Lock backlot, since the shooting script had been amended with a truncated version of the sequence. TARDIS scenes were taped on January 10th and 11th, followed by various inserts in the studio on the 13th, 16th and 17th. Footage of the bomber and of the exterior of the Doctor's plane was also captured on the 17th, on the premises of eCube Solutions at MOD St Athan. Finally, a pick-up shot of the United Nations meeting room as seen via the Doctor's sonic sunglasses was recorded at Roath Lock on March 17th.

The Pyramid At The End Of The World was scheduled for transmission on May 27th. The FA Cup final between Arsenal and Chelsea immediately preceded it, pushing Doctor Who to 7.50pm, twenty-five minutes later than Extremis the week before. On May 22nd, however, a suicide bomber representing the Islamic State terrorist group attacked fans as they left the Manchester Arena following a concert by singer Ariana Grande. Twenty-two people were killed and more than five hundred were injured in the explosion. Consequently, minor edits were made to The Pyramid At The End Of The World, eliminating references to terrorism as a possible cause of the global calamity foretold by the Monks.

• Doctor Who: The Complete History #87, 2018, “Story 271: The Pyramid At The End Of The World”, edited by John Ainsworth, Hachette Partworks Ltd.