When we last left the Doctor, he was once again refusing to regenerate after his encounter with the Masters and the Cybermen. He landed in the South Pole, 1986….where his first incarnation-who had also had his very first confrontation with the Cybermen-is pretty much doing the exact same thing, and encounters his future self.
The Twelfth of course realizes this, but the first Doctor just figures he’s another Time Lord, sent to recover the TARDIS and return it to Gallifrey.
The two are then interrupted by a World War I captain, who has somehow been ejected from 1914 in the middle of a standoff with a German soldier, and is confused by his sudden transportation and the strange dimensions of the Doctor’s (present) TARDIS. The First Doctor-finally realizing that the Twelfth is his future self-is equally confused as to the state of the TARDIS, considerably dirtier and darker than his version.
The TARDIS is then scooped up a massive spaceship, The Testimony, in a mysterious “Chamber of the Dead” piloted by a mysterious glass woman.
Bill Potts is also onboard, although the Twelfth Doctor is suspicious of her presence, considering the last thing he knew, she was turned into a Cyberman.
The First Doctor is likewise also confused at the current Doctor’s use of sonic devices, and ask that he observes with his own eyes, rather than tools-that the glass woman’s face is asymmetrical-like a real person’s. The entity then says it will take the Captain’s life in exchange for returning Bill to the Doctor. The Captain agrees, but the Doctor isn’t having it.
She also puts forward a little bubble clip show of the Doctor’s various lives, as well as nicknames, which horrifies the First Doctor quite a bit, although the Twelfth Doctor believes it’s been selectively edited: “They’ve cut out all the jokes!”
Also Believing that the Testimony might have sinister intentions, the Doctors and Bill leave the spaceship, temporarily leaving the current TARDIS behind and taking refuge about the First Doctor’s. Bill finds herself a bit offended by the first Doctor’s misogynistic attitude.
The Doctor decides he needs a sophisticated databank to learn more about the Testimony, but the databank in the First Doctor’s TARDIS is relatively empty at this point. After briefly considering Gallifrey’s matrix, he figures he needs another one-although it involves going into some dangerous territory-the planet Villengard, a place swarming with shell-less Dalek mutants. After one attacks the captain, the Doctors explore the city while Bill and the Captain wait in the TARDIS.
The Doctor comes to a tower where he chats with Rusty, the “Good Dalek” from “Into the Dalek” who has been fighting off his brethren but is still connected to their hive mind, a computer. Meanwhile, Bill leaves the TARDIS and talks with the first Doctor about his reasons for leaving Gallifrey and his purpose in the future.
The Doctor learns that “Testimony” is in fact an information archive using time travel to extract people moments before their death, and record their entire lives into a computer before returning them to their proper place with no knowledge of being taken out of time. That person can then also be resurrected into a glass copy. The Doctor figures that this isn’t evil, and it’s revealed that the Bill that’s been traveling with them is one such copy. However, when the Doctors met and each refused to regenerate, it caused a sort of paradox/”Timeline error” that wound up with the Captain popping into 1986.
The Doctors return the Captain to 1914, but the Doctor decides to cheat a little bit and place him during the Christmas truce, allowing him to live more of a life than he did originally. His name: Archibald Hamish Lethbridge-Stewart-and he asks for the Doctor to check on his family-the first Doctor promises he will, and the Twelfth knows he’s good for it (For obvious reasons).
Confident that his future is in safe hands, the first Doctor returns to his time and place in the snow, 1986, where he collapses and changes into his second self.
Meanwhile, his future incarnation wonders if he should continue to resist regeneration, and just die in his present form to finally get some rest from his very long life(s).
He chats with the glass avatar of Bill, which also gives him a present-it turns into Clara, and his memories of her-which were self-erased as he kind of went a bit too overboard to save her (getting Gallifrey pretty angry at him again).
A glass Nardole also shows up, saying it’s be kind of sad if the Doctor just died-The universe would suddenly go cold, as he puts it. After giving a goodbye hug to his companions (or rather their memories in glass bodies), he says he needs to make the final decision alone.
Figuring that the universe still needs saving, that they’ll get it wrong without him etc. the Doctor decides it’s time to once again regenerate. Before he regenerates, he gives some advice to his next incarnation.
You wait a moment, Doctor. Let’s get it right. I’ve got a few things to say to you. Basic stuff first.
Never be cruel, never be cowardly. And never ever eat pears! Remember – hate is always foolish…and love, is always wise.
Always try, to be nice and never fail to be kind. Oh, and….and you mustn’t tell anyone your name. No-one would understand it anyway. Except….
Except….children. Children can hear it. Sometimes – if their hearts are in the right place, and the stars are too. Children can hear your name.
But nobody else. Nobody else. Ever.
Laugh hard. Run fast. Be kind.
Doctor – I let you go.
And the process begins again. The usual fireworks, and the most damage he’s done to the console room since his tenth-to-eleventh change.
However, this time the result is a bit different….
The Doctor looks at HER reflection in the console room scanner. She is now a woman, appearence-wise in her mid thirties, and seems kind of excited at the prospect.
However, her excitement is a bit short-lived, as the damage to the TARDIS causes the console room to explode when she hits a button, and the doors to open in midair. Unable to get a hold, she falls out, thousands of feet in the air.
She’ll be back in October, though!