A message echoing through all of time and space emanates from the farming village of Christmas on the planet Trenzalore. With the assistance of Clara and Tasha Lem, pontiff of a mysterious religious order, the Doctor discovers that the signal is a message from Gallifrey, coming through a crack in time from another universe. Soon Trenzalore is under siege from massed hordes of the Doctor's worst enemies, as the spectre of the Time War is raised anew. Years give way to centuries, and it seems that the last days of the Doctor's final life are destined to be spent saving Christmas...

Having agreed to become its executive producer in late 2007, Steven Moffat began to formulate his plans for Doctor Who. He was determined to prevent the show from dwelling too much on its own past, and he soon developed the notion of tying the events of his first episode into the programme's future. When it briefly appeared that David Tennant might stay on for an extra season as the Tenth Doctor, Moffat proposed that his initial story would foreshadow the Doctor's regeneration at the end of the year. In April 2008, however, Tennant decided to stick to his original plan and leave Doctor Who alongside Moffat's predecessor, Russell T Davies.

Consequently, Moffat now had the opportunity to significantly expand his approach. He still envisaged the Eleventh Doctor's introductory adventure as being a consequence of events which emanated from his own future. Now, however, the complex storyline which developed from it would span not just a single season, but would be woven throughout the new Doctor's entire era, finally climaxing in the events surrounding his regeneration. From an early stage, Moffat's intention was to build to the revelation that the Doctor had become trapped in the midst of a vast war. Other details -- such as the relationship of this conflict to Gallifrey and the Time War -- would only present themselves over the years that followed.

The “oldest question in the universe” that was “hidden in plain sight”: “Doctor who?”

As such, Season Thirty-One's The Eleventh Hour did not merely mark the debut of Matt Smith as the Eleventh Doctor. It also introduced the mystery of the cracks in time which had spread throughout the universe, as well as the ominous assurance that “Silence will fall.” In the subsequent season finale, The Pandorica Opens / The Big Bang, the TARDIS appeared to explode as the result of the intervention of an unknown force, while many of the Doctor's enemies were brought together because they believed that he would be the cause of the universe's end. The Season Thirty-Two premiere, The Impossible Astronaut, was the first to feature the sinister creatures known as Silents. At some point, the Doctor's pregnant companion, Amy Pond, was kidnapped by their associate, the enigmatic Madame Kovarian. She tried to brainwash Amy's daughter -- who would become River Song -- to compel her to assassinate the Doctor, all to avert an unspecified war. In that year's finale, The Wedding Of River Song, another prophecy was uttered: “On the fields of Trenzalore, at the fall of the eleventh, when no living creature can speak falsely or fail to answer, a question will be asked, a question that must never, ever be answered.“ This was “the oldest question in the universe” that was “hidden in plain sight”: “Doctor who?”

From the start, Smith had suggested to Moffat that he wanted to limit his time on Doctor Who to three seasons. In mid-2012, however, Smith and Moffat agreed that the actor would stay for two additional specials beyond the end of Season Thirty-Three. The Day Of The Doctor would celebrate Doctor Who's fiftieth anniversary on November 23rd, 2013; a month later, Smith would exit the show in that year's Christmas special. Moffat therefore began to move his overarching storyline towards its final phase. The last story of Season Thirty-Three, The Name Of The Doctor, witnessed the discovery of the Doctor's tomb on the planet Trenzalore. Then The Day Of The Doctor revealed that the Time Lord planet, Gallifrey, had not been destroyed in the Time War as the Doctor had long believed, but had been hidden and lost in a pocket universe.

All of these elements would culminate in the Eleventh Doctor's last story. Here it would be shown that the Time Lords were reaching out through a crack in time, broadcasting a truth field and the question “Doctor who?”. Should the Doctor arrive and answer the question by speaking his real name, they would know that it was safe to re-enter the normal universe. However, the return of the Time Lords raised the spectre of the Time War reigniting, inspiring the creation of the Church of the Silence -- of which the previously-seen Silents were confessional priests -- to prevent the Doctor from answering the question. A breakaway chapter led by Madame Kovarian would seek to use time travel to eliminate the Doctor before he could arrive on Trenzalore, but would inadvertently create the cracks in time in the first place, as a result of their attempt to destroy the TARDIS.

The Christmas special would resolve the question of what happened when the Doctor ran out of regenerations

The difficult gestation of The Day Of The Doctor added an extra wrinkle to these proceedings. The anniversary special introduced a hitherto unknown Doctor who had fought in the Time War. As such, the Eleventh Doctor was really the Time Lord's twelfth incarnation -- pushing him precariously close to the thirteen-body limit which had been established in 1976's The Deadly Assassin. The Tenth Doctor had also used regeneration energy to create a half-human version of himself in 2008's Journey's End. Moffat now reasoned that this would count towards the overall total, making the Eleventh Doctor the last of the Doctors, although this would seem to contradict dialogue in some of his earlier stories. Consequently, the Christmas special would also resolve the question of what happened when the Doctor ran out of regenerations -- a conundrum which had vexed Doctor Who fans for many years.

Moffat completed his first draft of the Christmas special in mid-August. At this point, it was called “Twelfth Night”, in reference to the festival which celebrated the end of the Christmas season and had likewise inspired the title of the William Shakespeare play Twelfth Night, or What You Will, written around 1601. The notion of the Doctor being accompanied by a decapitated Cyber-head called Handles was inspired by The Pandorica Opens, in which the various body parts of a damaged Cyberman had been seen to act independently of each other. Moffat had been very pleased with the result, and had long hoped to revisit the concept. The sequence of Tasha giving away the fact that she was now a Dalek sleeper agent by offhandedly referencing her own death was an idea Moffat had originally planned to use for Darla in the Season Thirty-Three premiere, Asylum Of The Daleks.

Two elements were included to reflect events in Smith's life during the four months which separated the end of work on The Day Of The Doctor in April from the start of production on “Twelfth Night”. First, he had shaved his head for his role in the movie Lost River; this would force him to wear a wig for the Christmas special, and so Moffat decided to incorporate it into the narrative. Furthermore, Smith would be undergoing knee surgery shortly before the start of filming. Moffat therefore had the Weeping Angels injure the Doctor's leg, resulting in its eventual petrification and replacement with a prosthesis, and prompting the elderly Doctor to walk with a cane. References to the wooden leg would ultimately be deleted in editing, when it was decided that, because the artificial limb was never shown on screen, the detail felt superfluous.

During the regeneration scene, Moffat initially hoped to include cameo appearances by many of the Eleventh Doctor's friends. Apart from Clara, they included Amy Pond, Rory Williams, River Song, Brian Williams, Madame Vastra, Jenny Flint, Commander Strax, and Dorium Maldovar, as well as Craig Owens, his wife Sophie, and their son Alfie (otherwise known as Stormageddon). Later, these plans were scaled back, eliminating some characters but adding Barnable and Handles from “Twelfth Night” itself, before it was finally decided that only Amy would appear.

Jamie Payne initially strove for intimacy between the Doctor and Tasha Lem

By the end of August, the story was untitled. Its director would be Jamie Payne, who had made his Doctor Who debut on Hide for Season Thirty-Three. One of the decisions which confronted Payne and his cast would be the nature of the rapport between the Doctor and Tasha Lem, as played by Orla Brady. After initially striving for intimacy, it was decided that a more flirtatious approach suited the story best.

First on the recording schedule was the material at Clara's flat. Its interior was erected at Roath Lock Studios in Cardiff on September 8th and 9th, while the 10th saw Lydstep Flats in the city's Gabalfa district pose as its exterior. For the town of Christmas, cast and crew travelled to a FIBUA (Fighting In Built-Up Areas) village -- a Cold War-era mock-up of a West German hamlet used for simulated exercises -- at the Sennybridge Training Area in Sennybridge. Filming there began on September 11th and 12th.

With production having begun on a Sunday, Payne's team was afforded an early weekend on Friday the 13th and Saturday the 14th. Work at the FIBUA then concluded on September 15th and 16th. On the 17th and 18th, the top of the clock tower was erected within a disused factory at the Mamhilad Park Industrial Estate in Pontypool. September 19th saw Smith return to one of the first locations he had visited after joining the cast of Doctor Who: Puzzlewood, near Coleford in Gloucestershire, which had been used for Season Thirty-One's Flesh And Stone and now served as the forest on Trenzalore. The production then stood down for a three-day break, spanning Friday the 20th to Sunday the 22nd.

The remainder of the Christmas special was almost entirely filmed at Roath Lock, beginning with the clock tower basement on September 23rd and 24th. The first day also saw the recording of the puppet shows, plus the flashback to Season Thirty-Two's The God Complex -- revealing that the room containing the Doctor's greatest fear had hidden the crack in time -- while several inserts were taped on the second day. Work on the 25th began aboard the Dalek vessel. As with The Day Of The Doctor, various casings constructed over the preceding nine years were made available to Payne for the Christmas special. Furthermore, Mike Tucker -- who had built the first of the modern props for 2005's Dalek -- also permitted the use of a close replica he had fabricated for his own collection. The rest of the day dealt with the green screen shots of the Sontaran tank, and the start of work in the Papal Mainframe entrance chamber. The latter remained the focus on September 26th and 27th, alongside sequences aboard the Cyberman spaceship on the first day, and in both the TARDIS and the Mainframe corridor on the second day.

After the weekend, more action in the corridor set was filmed on September 30th. Later that day, Payne moved on to Tasha Lem's chapel, while also completing some pick-up shots. October 1st was spent back on the standing TARDIS set; in addition, various inserts were taped, as were the effects shots of the Silence adherents being unmasked as Dalek sleeper agents. Additional scenes in the chapel were recorded on the 2nd. That night, Payne invited the incoming Twelfth Doctor, Peter Capaldi, onto the TARDIS set in order to make himself comfortable prior to filming the regeneration scene the next day. October 3rd was dedicated to the special's closing moments in the console room, with Karen Gillan also present for her cameo as Amy Pond. Ironically, like Smith, she had shaved her head for a movie role -- as Nebula in Guardians Of The Galaxy -- and so she also had to don a wig for her return to Doctor Who. On this occasion, Jessica Davies provided the glimpses of the younger Amelia darting through the TARDIS; previously, the role had been played by Gillan's cousin, Caitlin Blackwood, but she now looked much older than when she had made The Eleventh Hour four years earlier.

October 4th was divided between material in the TARDIS and the chapel, and further inserts. The 5th was Smith's last day on Doctor Who, and was again spent in the TARDIS control room, although additional pick-ups were also captured. The last shots he performed were for the sequence of the Doctor trying to reach the external police box telephone. Nonetheless, recording for the Christmas special hadn't quite reached its conclusion. Producer Marcus Wilson had been delighted with the model filming undertaken for The Day Of The Doctor, and so three days -- October 14th to 16th -- were set aside for miniatures work on Smith's swansong. The shots achieved at Halliford Film Studios in Shepperton, Surrey included the regeneration energy overwhelming the Daleks, the destruction of a Christmas house, and a portion of the Dalek saucer's exterior.

In post-production, the voices emanating through the crack in time from Gallifrey were provided by Ken Bones, who had been the Time Lord General in The Day Of The Doctor. In light of the close connection between the Christmas special and the two preceding episodes, it was decided that it should be given a title which made this link explicit: The Time Of The Doctor. And then, on Christmas Day, Smith's time as the Doctor was up. But with Capaldi taking the reins -- and in light of his pedigree as both an actor and a longtime Doctor Who fan -- there had perhaps never been such anticipation for a new Doctor...

• Doctor Who Magazine Special Edition #38, Autumn 2014, “The Time Of The Doctor” by Andrew Pixley, Panini UK Ltd.
• Doctor Who: The Complete History #75, 2016, “Story 241: The Time Of The Doctor”, edited by John Ainsworth, Hachette Partworks Ltd.