The Doctor has retired to 1892 London. Despite the protests of former allies such as Madame Vastra, Jenny and Strax, he is determined to keep out of humanity's affairs. But one day, almost in spite of himself, the Doctor saves a barmaid named Clara from monstrous Snowmen made of sentient snow. Clara also works as a governess at the Latimer household, where the sinister Dr Simeon is abnormally interested in the frozen pond which was the scene of her predecessor's death. And there is another mystery afoot: Clara is the spitting image of Oswin Oswald, whom the Doctor saw perish in the Dalek asylum...

When it came to developing story ideas for his first two Christmas specials, Doctor Who executive producer Steven Moffat had sought inspiration in classic literature. 2010's A Christmas Carol was based on the Charles Dickens ghost story of the same name, while 2011's The Doctor, The Widow And The Wardrobe drew upon the children's fantasy novel The Lion, The Witch And The Wardrobe by CS Lewis. However, Moffat didn't want this practice to become routine, and he decided that the 2012 special would simply be set in the iconic Christmas environment of a snowy Victorian London, much like 2008's The Next Doctor.

In part, this setting was chosen in order to align with the emerging plans for the Doctor's new companion, following his permanent separation from Amy and Rory in the preceding story, The Angels Take Manhattan. During the autumn of 2011, the character was developed as a nineteenth-century governess named Beryl, who would meet a withdrawn and reclusive Doctor, retired from his adventures in time and space. The notion of the Doctor in seclusion was derived from an untitled idea proposed by former script editor Douglas Adams in 1979, which had been dismissed by then-producer Graham Williams.

Steven Moffat had held preliminary discussions about a spin-off series for Vastra, Jenny and Strax

Another benefit of the Victorian setting was that it would permit Moffat the opportunity to revisit a trio of characters he had originally introduced for Season Thirty-Two's A Good Man Goes To War. These were the Silurian adventurer Madame Vastra, her associate Jenny, and the Sontaran nurse Commander Strax; they had proved so popular that Moffat had held preliminary discussions with the BBC about developing a spin-off series for the characters, before he realised that his obligations to Doctor Who and Sherlock would preclude this. Actors Neve McIntosh, Catrin Stewart and Dan Starkey all confirmed that they were interested in reprising their roles -- although Starkey may have been somewhat surprised by the offer, given that Strax had died in his earlier appearance. Nonetheless, the idea of Strax serving as “a grumpy butler” to Vastra was derived from comments Starkey had made in the August 2011 issue of Doctor Who Magazine.

For the villain of the piece, Moffat turned to one of his favourite Doctor Who adventures: 1968's The Web Of Fear. Written by Mervyn Haisman and Henry Lincoln, it chronicled the Doctor's second encounter with the formless Great Intelligence and its robotic underlings, the Yeti. For the Christmas special, Moffat decided to pair the Great Intelligence with new servitors, who would take the more seasonally-appropriate form of malevolent snowmen.

Around the end of January 2012, the narrative underwent a significant shift. Concern had developed amongst the production team that Doctor Who would be hamstrung by the presence of an ongoing protagonist whose knowledge and perspective predated the audience by more than a hundred years. As such, it was eventually agreed that the new companion should come from contemporary London after all. The governess in the Christmas special would now be an alternative version of the modern-day character, as part of a story arc which would begin in the Season Thirty-Three premiere, Asylum Of The Daleks, and then culminate in its finale. The governess would now share the same name -- Clara Oswald -- as her modern-day counterpart; “Beryl Montague” became her alias although, in the broadcast episode, only the surname was mentioned.

Unusually, the 2012 Christmas special would be made in the midst of the production calendar

Since its inaugural edition in 2005, the Doctor Who Christmas special had usually been positioned first in the season's recording schedule. However, Season Thirty-Three was unusual in that it would be divided for broadcast into two blocks on either side of Christmas: five episodes would air in the fall of 2012 to conclude the adventures of Amy and Rory, with eight more held back until the spring of 2013 to chronicle Clara's time in the TARDIS. Consequently, the 2012 Christmas special would be made in the midst of the production calendar. At an early stage, it was planned to form Block Four, with filming to start in May. However, it soon became clear that Moffat's progress in writing the script was too slow to accommodate these dates. Hide was instead brought forward as Block Four, while the special would be paired with The Crimson Horror -- another story featuring Vastra, Jenny and Strax -- as Block Six. The director would be Saul Metzstein, who had also been responsible for the Block One stories Dinosaurs On A Spaceship and A Town Called Mercy.

Moffat finally completed a draft of the Christmas special in mid-June, at which point it was known as “The Snowman”. In fact, some consideration was given to omitting an on-screen title altogether, since it was thought that the title sequence might be held off until the end of the episode, signifying the Doctor's return to his old self. Early drafts incorporated another ingredient to the mystery of the Snowmen, associating them with sightings of driverless hansom cabs. There were also more flashbacks to Dr Simeon's early life. Medical equipment used in an unsuccessful attempt to revive the dying Clara was implied to be responsible for Strax surviving the events of A Good Man Goes To War. Moffat was also uncertain about an epilogue featuring the 2013 version of Clara, which was deleted and then reinstated more than once during the drafting process. When it was finally decided to preserve this scene, a false ending to “The Snowman” was concocted to safeguard the surprise; it saw Vastra and Jenny comment on how the events of the story had reinvigorated the Doctor.

In addition to the new companion, it was also planned that “The Snowman” would witness the debut of a completely redesigned TARDIS console room. Doctor Who was in the process of relocating from its former studio facilities at Upper Boat to its new home at Roath Lock in Cardiff Bay. There was no way to preserve the TARDIS set designed by Edward Thomas for Season Thirty-One's The Eleventh Hour, and so the current production designer, Michael Pickwoad, would have the chance to leave his own mark on the vessel's interior. Moffat indicated that he wanted to move away from the organic feel of recent console room sets and instead embrace the idea of the TARDIS as a machine, citing in particular its appearance during the Seventies.

Richard E Grant had played erstwhile Doctors on two previous occasions

Apart from Jenna-Louise Coleman as Clara -- who had already been cast for her appearance as another alternative Clara, Oswin Oswald, in Asylum Of The Daleks -- the other major new role in “The Snowman” was Dr Simeon. It went to Richard E Grant, who had played erstwhile Doctors on two previous occasions: first in Moffat's 1999 Comic Relief sketch The Curse Of Fatal Death, and then in the 2003 animated adventure The Scream Of The Shalka from BBC Online. Meanwhile, Francesca and Digby Latimer were portrayed by real-life siblings Ellie and Joseph Darcey-Alden.

Metzstein focussed on The Crimson Horror for the first few weeks of Block Six; the script for “The Snowman” was still being finalised at this time. Filming for the Christmas special ultimately began on August 6th and 7th, when scenes in the GI Institute boardroom were recorded at the Coal Exchange in Cardiff Bay. Several locations were used to represent Darkover House, the first of which was Fields House in Newport; material in the study was recorded there on August 8th and 9th. Work on the 10th began at Cathays Cemetery in Cardiff, which represented the graveyard where the nineteenth-century Clara was buried. Metzstein's team then shifted to Roath Lock for sequences in the hansom cabs. The next location to represent the Latimer residence was Treberfydd House in Bwlch, with action in the back garden and the hallway taped there on August 11th.

Sunday the 12th was a day off. On August 13th and 14th, Insole Court in Cardiff was the site of the playroom and the Latimer children's bedroom; the sequences involving Simeon's workmen shovelling snow were also taped there. The latter part of the 14th took cast and crew to Cardiff University, which provided the corridors and anteroom of the GI Institute. Metzstein also recorded an insert of the workmen outside the Rose and Crown pub. Then it was back to Treberfydd House from August 15th to 17th, for scenes in the front yard and corridors of Darkover House.

Following the weekend, Metzstein's team relocated to Bristol for two days. Various street scenes were filmed at St Nicholas Market on August 20th, and Portland Square was the area below the parked TARDIS on the 21st; also recorded were plate shots and footage to be added to the windows of the moving hansom cabs. Work on the second day was delayed when police were called to the nearby Cabot Circus shopping centre, where they executed a controlled explosion of an unattended briefcase in response to concerns that it might contain a bomb.

On August 23rd, the chase across the rooftop of Darkover House was taped at Roath Lock. The same day, recording began on two Moffat-scripted projects related to “The Snowman”. One was a prequel which would be broadcast during November's Children In Need charity event as The Great Detective. The other was destined for release through online retailers iTunes and Amazon in March 2013; it was meant to explain how Strax had survived his apparent death in A Good Man Goes To War and formed a partnership with Vastra and Jenny. Entitled The Battle Of Demons Run -- Two Days Later, it was directed by Doctor Who producer Marcus Wilson.

August 24th saw Llandough Castle in Llandough transformed into Vastra's orchid house. After another weekend of rest, August 27th found cast and crew at Treowen Manor in Dingestow, which served as the young Walter's house; the establishing shot of the Rose and Crown was also captured there. On the 28th, street and alley scenes were filmed at Roath Lock, while various inserts were recorded at Cardiff University. The rest of the week was spent in the studio, with the laneway behind the pub remaining Metzstein's emphasis on August 29th and the early part of the 30th. During the rest of the latter day, cast and crew were finally able to turn their attention to the brand-new TARDIS console room. Further shots inside the TARDIS were recorded on the 31st, alongside sequences on the cloud where the time machine was parked. On this set, mattresses were hidden beneath billows of dry ice to give the impression that the Doctor and Clara were actually traversing the cloud.

After the weekend, the scheduled end of principal photography on “The Snowman” was September 3rd. Metzstein's itinerary included the completion of the scenes outside the concealed TARDIS, plus material in the Doctor's cab. Some of the TARDIS footage was held over until September 17th. By this time, however, it had been decided that additional filming was required to complement or replace existing footage for the Christmas special. Following the end of Block Seven -- Journey To The Centre Of The TARDIS -- September 20th and 21st therefore saw several of the sets for “The Snowman” back in service at Roath Lock. Most notably, Metzstein captured several shots of Clara on the spiral staircase, alongside a number of additional inserts.

A new closing TARDIS scene saw the Doctor setting out to solve the mystery of Oswin and Clara

Various pick-up shots were then taped at Roath Lock on September 22nd, October 18th and November 9th; the latter included a new closing TARDIS scene with the Doctor setting out to solve the mystery of Oswin and Clara. Furthermore, with Grant, McIntosh, Stewart and Starkey all returning for the season finale, The Name Of The Doctor, there was now an opportunity to record extra material involving their characters. As such, Vastra and Jenny confronted Simeon at Insole Court on November 21st, and an insert for this sequence was taped at Roath Lock on the 23rd. Lastly, on the 28th, Vastra spoke to the Doctor over the phone from her living room, which was actually Merthyr Mawr House in Merthyr Mawr; this was a remount of material that had previously taken place in the orchid room.

In post-production, the name of the Christmas special was amended slightly to The Snowmen, and it was decided that both the title sequence and the episode title would appear in their customary place near the start of the broadcast. The opening credits were overhauled for The Snowmen, complementing the new companion and the new TARDIS interior. For the first time in twenty-first-century Doctor Who, they would feature a glimpse of the Doctor's face, as had been the case between 1967 and 1989. Murray Gold revised his arrangement of the theme music to suit the new opening credits.

On November 28th, a final major element was added to The Snowmen when Academy Award nominee Sir Ian McKellen recorded the Great Intelligence's dialogue. Beyond the widespread critical acclaim for his body of work, McKellen was popular with genre fans due to his involvement with the X-Men and The Lord Of The Rings movie franchises. Various material was discarded in editing. This included scenes involving a little boy (Max Furst) and his mother (Devon Black) who lived near the site where Simeon's labourers were working, as well as suggestions that the monsters were snowmen built the previous year which had now reformed. The coming of the Ice Governess was originally foretold when a shape appeared on the surface of the Latimers' frozen pond which resembled an upthrust hand.

Meanwhile, a third prequel to the Christmas special had been prepared from a script by Moffat. Entitled Vastra Investigates, it served to remind viewers of the background of Vastra, Jenny and Strax, while also hinting at a conundrum involving the snow, which seemed to be falling from a cloudless sky. A scene in Vastra's carriage was recorded by Metzstein at the Coal Exchange on November 16th, during work on The Name Of The Doctor. The bulk of the mini-episode, set in a Victorian house where Vastra had just solved a mystery, was filmed on November 29th at the Mansion House on Richmond Road in Cardiff, under director John Hayes. Running one hundred and sixty seconds, Vastra Investigates was released via the BBC's Doctor Who website on December 17th.

• Doctor Who Magazine Special Edition #37, Autumn 2014, “The Snowmen” by Andrew Pixley, Panini UK Ltd.
• Doctor Who: The Complete History #72, 2017, “Story 231: The Snowmen”, edited by John Ainsworth, Hachette Partworks Ltd.