The Doctor and Nardole have spent years in seclusion at St Luke's University in modern-day Bristol, guarding a secret vault. But despite his intention to remain hidden, the Doctor can't resist taking a bright young canteen worker named Bill Potts under his wing. Bill has struck up a tentative relationship with Heather, a melancholy student who has a star-shaped defect in one eye. Heather is fascinated by a remote part of campus, where a strange puddle never evaporates. When Heather is transformed into an entity made entirely of water, Bill finds herself implacably pursued... and the Doctor is forced back into action.

Although Steven Moffat had anticipated that 2015 would be his final year as Doctor Who's executive producer, things did not work to plan. By the summer, former Doctor Who scriptwriter Chris Chibnall had been identified as the preferred candidate to succeed Moffat. The production dates for Season Thirty-Six were delayed until the summer of 2016, and its broadcast to the spring of 2017. This would permit Chibnall to assemble his own team -- including a new companion, since Jenna Coleman's Clara Oswald would be exiting in the Season Thirty-Five finale. However, it gradually became clear that Chibnall would not be available within this timeframe, due to his commitments to a third and final season of his mystery drama Broadchurch. Instead, Moffat agreed to remain at the helm for an extra year, overseeing the 2016 Christmas special and a new twelve-episode run for 2017.

As a result, the Doctor's next companion would now be Moffat's to devise and cast. He had already decided against introducing such a character in the 2015 Christmas special, The Husbands Of River Song, since it was meant to be his swansong and -- apart from Peter Capaldi's Twelfth Doctor -- he had wanted to give Chibnall a clean slate. Furthermore, Season Thirty-Five had seen the first signs of fatigue in Doctor Who's twenty-first-century viewing figures, and so Moffat decided that the 2016 Christmas special -- eventually The Return Of Doctor Mysterio -- was also an unsuitable place for her debut. Instead, Season Thirty-Six would begin with a reboot of the series format, to make it more inviting for new and lapsed audiences. The incoming companion would be part of this approach: a bright and funny everywoman, who would stand in contrast to Clara's initial manifestation as a puzzle for the Doctor to solve, and her later development into a human approximation of the Doctor himself.

Steven Moffat thought that the mysterious vault might contain either Missy or Davros

The revised status quo into which the companion would be introduced was partly inspired by Educating Rita, a 1980 play by Willy Russell about the rapport between a cynical tutor and his student, a hairdresser who had decided to go back to school. Moffat had seen it in 1982, when the tutor was played by the former Fourth Doctor, Tom Baker, and he now felt that a similar relationship would be an interesting twist on the normal Doctor-companion dynamic. Moffat imagined that the Doctor might have taken up a post at a university in order to keep watch on the occupant of a mysterious vault. At this stage, he thought that it might contain either Missy, the female version of the villainous Master whom he had introduced during Season Thirty-Four, or Davros, the creator of the Daleks. Both characters had last appeared in the Season Thirty-Five premiere, The Magician's Apprentice / The Witch's Familiar.

By the end of 2015, it had been agreed that only actresses of colour would be considered for the new companion. Even latterly, Doctor Who had rarely paired the Doctor with non-white associates, and Moffat felt that the production team had to make more of an effort to reflect a greater on-screen diversity. Auditions for the character began in early 2016, with about fifty performers under consideration. The codename “Meantown” was used to preserve secrecy; this was an anagram of “Woman Ten”, alluding to the fact that Season Thirty-Six was the tenth since Doctor Who's revival in 2005. Moffat wrote three audition pieces to help whittle down the potential candidates to play the character, who had now been dubbed Bill. Ironically, this was a reference to the nickname for actress Billie Piper, who had played companion Rose Tyler; Moffat had heard it used by the Tenth Doctor, David Tennant, during the making of 2013's The Day Of The Doctor.

On January 22nd, the BBC confirmed that Chibnall would be replacing Moffat as Doctor Who's executive producer with Season Thirty-Seven. The delay in the transmission of Season Thirty-Six to the spring of 2017 was revealed at the same time. The five finalists for the role of Bill were given the opportunity to act opposite Capaldi on March 8th. Within a week, it had been offered to Pearl Mackie. Originally spotted by casting associate Ri McDaid-Wren, Mackie's work to date had largely been in the theatre; indeed, she was then appearing in The Curious Incident Of The Dog In The Night-Time in the West End. On April 7th, Capaldi decided to attend a performance in order to better acquaint himself with his new co-star. When he was unexpectedly invited backstage after the show, Capaldi and Mackie had to pretend to be unfamiliar with each other, lest they give away the new companion's identity!

To bridge the gap in Doctor Who's transmission, Charlotte Moore suggested the creation of a mini-episode to introduce Bill

Meanwhile, Charlotte Moore, BBC One's Controller of Programmes, had met with Moffat's fellow executive producer, Brian Minchin, to discuss the manner in which Mackie's casting would be revealed. The absence of Season Thirty-Six from the 2016 schedule meant that Doctor Who would be on hiatus for a longer period than at any time since 2005. Moore suggested that a way to bridge this gap and reinforce Doctor Who's importance to the Saturday schedule was to create a mini-episode which would introduce Bill. She offered a broadcast slot at halftime during the FA Cup semi-final on Saturday, April 23rd.

Moffat hastily reworked one of the audition pieces -- in which Bill encountered the Daleks for the first time -- as the script for the mini-episode, which became known as Friend From The Future. He allowed for the possibility that its events might eventually be incorporated into a Season Thirty-Six story, but he didn't feel that this would be essential. By this time, Doctor Who newcomer Lawrence Gough had been booked to direct Block One of the year's recording schedule, which would consist of the first two episodes. He also oversaw Friend From The Future, which was recorded at Roath Lock Studios in Cardiff on April 13th. Apart from Capaldi and Mackie, the only other castmember was Jon Davey, who operated a bronze Dalek casing originally constructed for Season Thirty-Three's Asylum Of The Daleks. Footage taped for Season Thirty-Four's Into The Dalek was incorporated into Friend From The Future, which ran to one hundred and twenty-two seconds.

In addition to Bill, Moffat felt that the new university set-up would benefit from the presence of a second supporting character, who could act as a factotum to the Doctor in the manner of Alfred Pennyworth, Batman's butler in various comic books and spin-off media. He was still pondering this addition in early 2016 when he received a message from Matt Lucas, who had played the bumbling Nardole in The Husbands Of River Song. Lucas had relished his time on Doctor Who and, although the story had ended with Nardole reduced to a disembodied head sharing a robot body, he indicated that he would be keen to return if the opportunity presented itself.

Since Nardole's origins were obscure, Moffat felt that the character could easily be restored and feature prominently in the Season Thirty-Six premiere. He then envisaged a handful of additional cameo appearances during the rest of the year, which could perhaps be filmed together to fit into Lucas' busy schedule. The actor soon confirmed his interest, and even indicated that Nardole could have a greater presence in the season than Moffat had anticipated. Indeed, he had turned down a television pilot in Hollywood in order to make himself available to Doctor Who.

Steven Moffat expected that Heather would return in the season finale to help wrap up Bill's story

Moffat was writing the script for the season premiere, entitled “A Star In Her Eye”, during the spring of 2016. The highlight of the story was the Doctor's emerging relationship with Bill Potts; Moffat wanted the alien threat to be a simple one which could sit in the background. Although one of the audition pieces had referred to Bill's romantic interest in a boy, Moffat now decided that an attraction to girls suited her better. As such, he developed Heather, whom he expected would return in the finale to help wrap up Bill's story; the arc of the season was still being planned with a view to giving Chibnall the freedom to mould the show to his designs. Moffat only subsequently realised that the names Bill and Heather echoed those of William and Heather Hartnell: the actor who played the First Doctor and his wife. The main setting -- which would be revisited throughout the season -- was the fictional St Luke's University in Bristol. It was named in reference to Luke the Evangelist, author of one of the four canonical Gospels of the Bible, who was the patron saint of physicians and surgeons, and was generally believed to have been a physician himself.

The chase sequence in “A Star In Her Eye” gave Moffat an opportunity to incorporate elements from Friend From The Future. At the suggestion of regular Doctor Who contributor Mark Gatiss, the spaceship was established as belonging to the Movellans, robotic enemies of the Daleks who had appeared in 1979's Destiny Of The Daleks. By late May, Moffat had revised his script to eliminate virtually all of the dialogue which had actually appeared in the mini-episode, since he worried that it would now seem out of place if it no longer functioned to establish Bill's character. As a result, the connection between Friend From The Future and “A Star In Her Eye” would now largely be by implication. On June 14th, the BBC confirmed that Matt Lucas would be reprising the role of Nardole during Season Thirty-Six.

The start of Block One marked the first recording on Doctor Who since the completion of The Husbands Of River Song nine months earlier. To the greatest extent that was feasible, Gough arranged his shooting schedule to make “A Star In Her Eye” in chronological order, which he thought would help Mackie adjust to her character. The first scenes to be recorded, from June 20th to 22nd, were those in the Doctor's office. Constructed at Roath Lock Studios in Cardiff, it was designed to be an old-fashioned lecturer's study, in contrast to the modern feel of the rest of St Luke's University. This was a change from Moffat's original conception of the institution, which resembled Hogwarts -- the magical boarding school in JK Rowling's Harry Potter novels -- before it was decided that such a setting would seem too elitist. The exterior spaces at St Luke's were found on the grounds of Cardiff University. Work there took place on June 23rd and 24th; amongst the various locations utilised by Gough's team, the window looking into the Doctor's office was situated in the campus' Main Building.

Matt Lucas and Steven Moffat agreed that Nardole would now be portrayed with a greater sense of nuance

After the weekend, work at Cardiff University was completed on June 27th, when Lucas rejoined the programme. He and Moffat had agreed that Nardole would now have to be portrayed with a greater sense of nuance, since the buffoonish portrayal of his first appearance would become insufferable on a recurring basis. Part of the 27th was also spent elsewhere in Cardiff, capturing a shot of the clock at City Hall and then recording Bill running back to campus along High Street. On the 28th, scenes outside the vault were taped at Roath Lock; like the Doctor's office, this set would appear again in subsequent episodes.

June 29th saw scenes in the Australian diner and its washroom filmed at the Lookout Café, part of World of Boats on Cardiff Bay. This work continued to the morning of the 30th, with a green screen providing the illusion that the venue actually had a view of the Sydney Opera House. The rest of the day took the cast and crew to Taff's Well Quarry in Taff's Well, which served as the surface of the alien world. It was back to Roath Lock on July 1st, when Gough's itinerary included more material in the Doctor's office, footage in Bill and Moira's house -- actually a standing set used for the Welsh-language soap opera Pobol y Cwm -- plus various effects and pick-up shots, before another weekend off.

The only part of Bill's house that wasn't repurposed from Pobol y Cwm was the hallway leading to her bathroom; this was a new set constructed at Roath Lock, with the sequence taped on July 4th. The rest of the day was spent on the Llandaff campus of the Cardiff Metropolitan University, where the Atrium Café posed as the canteen where Bill worked. The 5th saw cameras rolling at two Cardiff locations. First, Clwb Ifor Bach stood in for the student bar where Bill initially met Heather, as well as the club from which Moira phoned Bill. Next, the Doctor addressed his class at the Reardon Smith Lecture Theatre, part of the Nation Museum of Wales. Many of the students in attendance were actually staffmembers at the Doctor Who Experience, a permanent exhibition on Cardiff Bay.

The spaceship sets constructed for Friend From The Future had now been modified and re-erected at Ffilm Factory 35, part of the Sony UK Technology Centre in Pencoed. Work there spanned July 6th and 7th, with a second Dalek built for Asylum Of The Daleks joining the casing which had appeared in the mini-episode. In addition, the latter day saw work at Roath Lock, including the green screen effect of Heather showing Bill the universe, plus Bill entering the TARDIS for the first time. Inserts were also taped at both studios.

Gough then turned his attention to episode two, Smile, although some footage for “A Star In Her Eye” remained to be filmed at Roath Lock. More TARDIS sequences were taped on July 11th, followed by inserts on July 12th and September 6th. A new scene was also shot on the latter day, with the steps built as part of the Thames riverbank for episode three, Thin Ice, now used as the stairs descending from the Doctor's office. Finally, September 15th saw an additional pick-up shot -- of Bill's eyes in the puddle -- recorded on the studio grounds.

The star-shaped defect in Heather's eye was originally meant to be achieved using a contact lens, but the discomfort experienced by actress Stephanie Hyam prompted a change of plans, and it was instead accomplished digitally. By early 2017, Moffat had soured on the title “A Star In Her Eye”, in part because Gatiss had observed that it brought to mind the talent show Stars In Their Eyes. Since the premiere was effectively acting as the pilot episode for a new approach to Doctor Who, it was renamed The Pilot, which was also how the alien intelligence referred to Heather. Meanwhile, during a January 30th appearance on Jo Whiley's BBC Radio Two show, Capaldi announced that he would be leaving Doctor Who alongside Moffat and Minchin following the 2017 Christmas special. This would give Chibnall free rein to determine the direction that the programme would take under his aegis.

The transmission of Season Thirty-Six got under way on April 15th, with The Pilot scheduled at 7.20pm between Pointless Celebrities and Casualty. The timeslot had most recently been occupied on a regular basis by the ninth season of the quiz show Who Dares Wins. The Pilot was also available in select cinemas, with screenings in Australia and New Zealand on the 16th and 17th, and in the United States on the 17th and 19th. The American presentations were accompanied by For Tonight We Might Die, the first episode of the spin-off series Class, which had originally aired the previous October and included an appearance by Capaldi as the Doctor.

• Doctor Who: The Complete History #85, 2018, “Story 265: The Pilot”, edited by John Ainsworth, Hachette Partworks Ltd.