The pair are approached by a confused and injured First World War British captain, displaced from 1914 while in a gun-point stalemate with a German soldier.

Upon encountering the ship's glass-like holographic pilot, they are offered freedom in exchange for the Captain returning to the moment of his death.

The Doctor learns that the pilot and its ship, known as Testimony, are designed to extract people from their timelines at the moment of their death, and archive their memories into glass avatars.

The Twelfth Doctor explains to the First that he deliberately shifted the Captain's timeline forward to the start of the Christmas truce, to ensure his life would be spared.

As the time rotor and the console room explode, the Doctor falls out of the tumbling TARDIS, which dematerialises as she plummets to Earth below.

This happened in the 2010 special "The End of Time", when Moffat took over for Russell T Davies in the final moments of the episode, writing Matt Smith's first words as the Eleventh Doctor.

[3] The change in showrunners almost caused the annual episode to be cancelled, as Moffat planned to leave after the tenth series finale and Chibnall did not want to begin his run with a Christmas special.

When he learned of Chibnall's plans, Moffat elected to stay long enough to produce one final episode, as he was concerned that the show would lose the 25 December slot in the future if it missed a year.

[4] In an interview following the episode's broadcast, Gatiss said he cried at the thought of playing the Brigadier's grandfather when he finished reading the script.

Reportedly Derek Martinus, the director of The Tenth Planet, cut a line from the original script which suggested that the Doctor was refusing to undergo the regeneration process.

[11][12] On 30 January 2017, Peter Capaldi confirmed that the tenth series would be his last as the Twelfth Doctor, and that he was set to leave after the 2017 Christmas special.

[14][15] David Bradley appears as the First Doctor, having previously portrayed William Hartnell in the 2013 docudrama An Adventure in Space and Time.

[20] Bradley later voiced the First Doctor in many audio dramas for Big Finish Productions alongside his co-stars from An Adventure in Space and Time.

[21] The first trailer for the episode was shown during the 2017 San Diego Comic-Con, revealing the return of Polly, a companion from the end of William Hartnell's tenure as the First Doctor, portrayed by Lily Travers,[22] and Pearl Mackie as Bill Potts.

[24][25] It was later confirmed that Ben Jackson, a companion of the First and Second Doctors, who served alongside Polly, would also feature in the episode and that he would be played by former Hollyoaks cast member Jared Garfield.

During his speech the Doctor paraphrases philosopher Bertrand Russell when he advises his future self that "hate is always foolish and love is always wise".

The cinema release includes two bonus features: a behind-the-scenes view of the episode, and a special celebrating the tenure of Peter Capaldi as the Doctor and Steven Moffat as showrunner and lead writer.

He also praised the casting of Mark Gatiss as the Captain feeling that he " provides the perfect element of humanity required for a Doctor Who story".

[53] Writing for Vulture Ross Ruediger praised the episodes use of nostalgia and how it concluded the Twelfth Doctor's character arc.

[56] Michael Hogan offered a negative review for The Daily Telegraph, criticising Moffat's writing and concluding that viewers "would have been left scratching their heads in bafflement.

"[61] Den of Geek's Pete Dillon-Trenchard reported that this was a controversial aspect of the episode, even in the pre-publicity, but they "found it hard to find any examples of sexism as egregious as the ones shown here.