.jpg)
The First Doctor is at the South Pole. After an encounter with the Cybermen, he is injured but refuses to regenerate. He fights off the change and walks out into the snow and as he's walking back to the TARDIS he encounters the Twelfth Doctor who is also refusing to regenerate following an encounter with the Cybermen. The Twelfth Doctor recognises the First Doctor but the same can't be said for the other way around. Twelve doesn't remember fighting off the change as One and presses him to understand that he needs to regenerate and carry on. But their conversation is interrupted as the snow around seems to freeze in place and a confused and injured World War One British military captain approaches them, asking for a doctor. Twelve realises that something has gone very wrong with time.
The Captain had been in December 1914 in a ditch in a gun-point stalemate with a German soldier when time froze. He walked up out of the ditch and spots a mysterious glowing figure that turns around and displaces him while claiming there is a timeline error. When he came to he was at the South Pole surrounded by snow frozen in the air. This is when he approached the Doctors and asked them for help, disoriented from his journey.
The trio head into the TARDIS together where One finally realises that Twelve is a future regeneration. After a bit of discussion they end up being abducted by a large spaceship where Bill is already waiting. The Doctor is skeptical that this could really be Bill since she had been turned into a Cyberman. She then tells the Doctor how the girl from the puddle had come from her but when questioned, she doesn't remember how she got onto the ship or where her girlfriend has disappeared to. They then encounter a glass figure that is the personification of a computer system that demands the Captain be turned over for Bill to be freed. The Captain offers himself up but Bill doesn't want the Captain to be captured on her account. Bill encourages Twelve to save the world and he becomes inspired to find out who the glass figure is and will stop them if he doesn't like it. The glass figure brings forth bubbles of all the different regenerations of the Doctor and announces all the names he has known over the years. One is overwhelmed by this swam of knowledge but Twelve sets off the release of the TARDIS and undoes the chains to release them. The group is able to drop down to get on top of the TARDIS from which they jump down while Twelve's TARDIS is pulled back up into the ship.
The group escapes into One's TARDIS and it takes them to the planet Villengard which is located in the centre of the universe. Bill is amazed to learn that she in the presence of one of the past regeneration of the Doctor. Twelve determines that they should try to figure out what the original face is that the glass figure is modelled after. They are searching for answers on the origins of this latest threat. Twelve encounters the rogue Dalek Rusty, who is hiding out from the other Daleks hunting for it. Twelve convinces Rusty to give him access into the Dalek Hivemind for all the data contained within it.
Bill is revealed to be a Testimony avatar created from her memories. The glass pilot and its ship are known as the Testimony created on New Earth. They were created in order to extra people from their timelines at the moment of their death so their memories could be channeled into glass avatars. It wasn't something designed with a malicious intent, leaving Twelve confused about what to do. He is also conflicted on his feelings regarding Bill and whether it is really her. The philosophical dilemma is whether or not a collection of memories amounts to a person's existential identity.
The Doctors see that there is no evil foe for them to fight and acknowledge that they were the ones that caused the time error that displaced the Captain to where they were. By trying to refuse to regenerate, they created a whirlpool through time. They decide to return the Captain to his timeline, with Twelve remembering that everyone is important to someone. As they drop the Captain off to the moment in the ditch where he will meet his demise. The Captain asks the Doctors to look after his family and introduces himself as Archibald Hamish Lethbridge-Stewart. He will have no memory of his experiences with the Doctors and all the visitors to his timeline will be rendered invisible when time resumes. Archibald is an ancestor of the Doctor's close friend, the Brigadier.
Once time resumes, the Doctors watch the stand-off carry on but it's then that soldiers on both sides of the conflict begin to sing "Silent Night". This causes the fighting to stop and the stand-off stops, as the men agree to put aside their differences for now since it's Christmas. Twelve tells One how he had shifted the Captain's timeline so this stand-off would be happening on Christmas and save the Captain's life. Only on Christmas could such a miracle have taken place and the opposing soldiers would agree to come together and stop their fighting. The Captain calls for medical attention to tend to the injured German soldier that had been about to shoot him.
One says goodbye to Twelve, now feeling at peace with his decision to regenerate. One wishes Twelve luck and heads back to his TARDIS where he resumes his regeneration and is returned to the South Pole. Twelve reunites with Bill's avatar and insists that she is not the real Bill. She replies with a further explanation that memories are what define a person. She further emphasises her point by leaving him with a goodbye present, that of returning his memories of Clara Oswald. An avatar of Nardole appears next but the Doctor still won't give over the testimony of his life to the avatars. He hugs them both goodbye and they leave him to be alone in his final moments. He goes back into the TARDIS and prepares a bit of advice for his next incarnation before regenerating.
The Thirteenth Doctor gazes upon her new reflection, amazed by what she sees. But when she tries to start the ship, it malfunctions badly due to damages caused by her most recent regeneration. The doors to the TARDIS open and it falls on its side. Despite her best efforts to hold on, the console room suffers an explosion and she falls out towards the Earth, watching as the ship dematerialises in space.
Doctor Who will return for series 11 in 2018 on BBC One.
