The Doctor Falls (TV story)

The Doctor Falls was the twelfth and final episode of series 10 of Doctor Who.

It saw the departures of both Bill and Nardole, and the events leading to the Saxon Master's regeneration into, with the Master being mortally wounded by his female successor. However, he in turn kills her, bringing an apparent end of the Master's life. The episode also explained the different and conflicting origins of the Cybermen appearances, citing it to "parallel evolution".

Expanding on the Twelfth Doctor's regeneration teased in the previous episode, it saw him mortally wounded in battle against the Cybermen. However, the Doctor managed to postpone the change, expressing how he was sick of "always having to be someone else", leading into the arc of the next episode.

Most notably, the final scene of the episode featured the unexpected return of the First Doctor, now portrayed by David Bradley, in a scene set during the events of The Tenth Planet itself, the first time an incarnation of the Doctor from the classic series had appeared since the series was revived in 2005 and not been played by his original actor. Bradley had previously portrayed William Hartnell in the docudrama An Adventure in Space and Time.

Synopsis
As he struggles to resist regenerating, the Twelfth Doctor prepares to make a last stand against the ever-growing army of Cybermen. However, with Bill still a Cyberman, and gradually turning to her old wicked ways as  reminds her of who she used to be, can the Doctor convince his old friend to finally be good before he falls?

Plot
The episode opens on a group of farmers, adults and children, on Floor 0507 facing against the prototypes from Floor 1056, dubbed "scarecrows", shooting them down by night to then restrain them on wooden crosses by day. A school child named Alit is out in the field one morning when a shuttlepod blasts through the ground, crashing near her. As the smoke clears, a Cyberman emerges from the wreckage carrying an unconscious Doctor.

Sometime earlier, the Doctor awakes on top of the hospital, now restrained in a wheelchair, soon recalling how he was subdued by and. The Master and Missy dance and flirt, with him asking if she's his next incarnation; Missy guesses she is as she can't remember what caused her to regenerate. The Master is stunned: "I'm going to turn into a woman, and you can't remember it happening?" Missy wonders if she is a woman; the Master confirms it. Though the Master doubts it, the Doctor begins deducing what he's been up to since he vanished while blasting Rassilon with his life energy.

Upon getting back to Gallifrey, the Time Lords, grateful for the Master's help in preventing Rassilon from executing The Final Sanction, properly restored his body. With that done, the Time Lords kicked him off Gallifrey. However, the Master stole a TARDIS to go back into the universe; so he considers it a mutual being kicked out. After that, the Master landed on the colony ship, lived like a king and killed people at his leisure. However, the colonists eventually overthrew him and the Master attempted to flee. However, as his TARDIS was on the last level, too close to the event horizon, it burned out his dematerialisation circuit and left him stranded. "You never could drive could you?" the Doctor asks.

Both the Master and Missy are insulted; she asks her earlier self if he has any requests as to how to torture the Doctor. The Master suggests dropping the Doctor off the roof; Missy is against the idea, saying that they'd be "up and down the stairs all night" because she doesn't know how many regenerations the Doctor has. Missy and the Master look over the roof, seeing people march like mindless sheep into the hospital to be turned into Cybermen. They taunt their old friend by telling him of their plan of the Cybermen converting all the humans on the ship. Missy asks the Doctor if he's impressed. They mockingly call the Doctor "granddad", reminding him that Bill is now a Cyberman.

The Doctor tells them that after all this time if they still think they're winning when he's in the room, they're missing something obvious. Hearing the Cybermen advancing, Missy looks over the ledge and quakes in horror; the Cybermen are coming for them. The Master is confused, as these Cybermen are primitive and shouldn't even be attempting to convert non-humans.

The Doctor explains that when he was knocked down by Missy, he altered the signal of the Cybermen so they would convert two-hearted beings as well, hence why they are now focusing on the Time Lord's presence. The Masters panic, Missy frantically using her sonic umbrella to lock a metal door to hold back advancing Cybermen while the Master uses his laser screwdriver to destroy advancing Cybermen. The Doctor brags that he is the only one who is able to stop so many Cybermen at once. Realising this, a conflicted Missy knocks the Master out and frees the Doctor from his restraints. The Doctor starts wondering which side she is on to which she admits her indecisiveness as she is confused and her other half is unconscious.

The Doctor uses his sonic screwdriver to contact Nardole, who reveals he has commandeered a shuttlecraft. Nardole lands near the roof to help escape, but the Doctor is grabbed and electrocuted by a Cyberman before he boards. Missy tries to save him using her other self's laser screwdriver but Bill, in her cyber form, intervenes first, destroying the Cyberman with a blaster based on her head and the Doctor recognizes her before collapsing to the ground unconscious. Missy and the Master try to convince Nardole to abandon the Doctor "The Doctor's dead; he told me to say he always hated you," they both say. However, Bill prevents the shuttle from leaving, grabbing the ladder until they rescue him. The Doctor regains consciousness and promises Bill that he will find a way to return her to normal.

They escape to Floor 0507, where time moves slower. They find themselves on a solar farm, the Master deducing such by the holographic sky, where some of the humans and a large number of children protect themselves from the early Cybermen prototypes from Operation Exodus. Nardole approaches Alit, declaring they will need her help. They spend two weeks there while the Doctor recovers from his injuries.

Bill awakes in the barn, unsure why the villagers are scared of her, concerned why she can't see the Doctor. When given a mirror by Alit, she becomes horrified to discover she was converted into a Cyberman. Alit goes to run but bumps into the Doctor who thanks her for being kind to Bill, offering her a jelly baby as she leaves. The Doctor has somewhat recovered, though he still has a scar from where he was hit by the Master and is clearly in a lot of pain but trying to hide it.

Trying to console Bill, she gradually realises that though she thinks she is human, she is still a Mondasian Cyberman in appearance. She grows angry, the Doctor backing away as Bill accidentally triggers the blaster on her head, igniting the door on the barn, causing an explosion. Nardole, who has been preparing the town for the oncoming Cybermen despite one woman saying he has been working them too hard, passively tells the farmers not to worry; they have an upcoming war to focus on.

Bill sheds a tear when she realises the humans are frightened of her, and the Doctor wipes it away, noting it unusual. The Master tells the Doctor that he and Missy have been working on something, and pauses briefly to mock Bill, chastising the Doctor for still referring to her as a female and taunts how he hated the time he had to spend with Bill as "Razor". He stops because Bill claims he is not upsetting her, though she cries beneath her mask when he leaves. The Doctor finds it odd she is still able to shed tears. While traversing after the Master, the Doctor struggles to walk, limping heavily. He briefly stumbles against a tree, regeneration energy attempting to trickle from his hand (revealing that his electrocution by the Cyberman on the roof was fatal, and his body is preparing to regenerate). Wanting to not worry Bill, he draws up a stick and carries onwards but Bill is still distraught that the Doctor can't fix her current condition, the Doctor responding "where's there's tears; there's hope."

They soon reach the middle of a forest, just after the Master and Missy theorise they can't retain their memories as their timelines are out of sync. Missy briefly displays empathy for Bill's condition, something the Master finds disgusting. Missy reveals she has discovered a camouflaged lift in the nearby forest, with which she suggests they can escape to Floor 0000, using her sonic umbrella to call it. However, the Doctor declares that there will no doubt be a Cyberman in the lift waiting to find their floor, as the lift was taken to the bottom by them previously. Understanding this, Bill orders them to stand aside, the Doctor convincing the two Masters to do so.

The three Time Lords prepare behind Bill, drawing their respective devices. As guessed, the lift brings up an advanced Cyberman from the lower floor, Bill speedily firing on it with her cyber blaster, the Master following likewise with his laser screwdriver as the Doctor and Missy use their sonic devices to slow its advance with a barrier. After several seconds, they disable it.

With their position given away, the Master and Missy both wish to use the elevator to go to the bridge and escape in the Doctor's TARDIS, but the Doctor informs them that the time differential between top and bottom of the ship would give the Cybermen ample time to stop them, meaning there isn't a safe way to return to the TARDIS. The Doctor figures that the Cybermen will now have much more time to plan, given they now know what floor they reside on, they must prepare for a battle. He returns to the village, revealing the alarm they now hear is the Cybermen's warning from the lower floors. Using a computer, Nardole discovers that the floor below this one has many fuel pipes that he can detonate as weaponry against the Cybermen, briefly testing such by blowing up a windmill, stunning the villagers; the Doctor remarks that they can use such to confuse the Cybermen and make them believe they are stronger than them. The Doctor finds a conduit to another solar farm on a higher floor that can be used to evacuate the children, having Bill blast it open, knowing this is a fight they will likely lose.

Meanwhile, the Master and Missy decide to leave and plan to find the Master's TARDIS at the lowest floor, though the Master reveals he broke his TARDIS. Missy shoves convinces her younger self to always keep a dematerialisation circuit on hand. She recalls the time a woman shoved her against her a wall to convince her to carry the device on her at all times. While recalling the story she shoves the Master against the wall, revealing herself as the one to convince the Master to carry the circuit. The Master says "Is it bad that I.. er-" hinting at a slight sexual arousal of his future incarnation, but Missy just retorts that it's very wrong. Night falls, the Doctor standing guard outside the house. Inside, a woman attempts to flirt with Nardole as he works on his computer, only to turn around and shoot at Bill, falsely thinking her a hostile Cyberman. She leaves distraught, going outside to find the Doctor. The first wave arrives, Nardole and Alit preparing to combat them, successfully tricking them that an apple was capable of destroying an entire group of them. They retreat to the house, now understanding the Cybermen will likely return to outright destroy them next time rather than merely capture them for conversion.

Meanwhile, the Doctor notices the two Masters trying to leave and runs after them. He pleads for them to be by his side to help. He gives an emotional and passionate speech on why he helps people, since it isn't easy or always going to work, it is just the right thing to do, as saving people would just be kind. The Master ridicules the idea, saying that he didn't listen to a word the Doctor said. However, Missy was somewhat moved by the Doctor's speech, agreeing that being the Doctor's friend was what she always wanted. However, after briefly grabbing each other's hand, she sides with her predecessor. At the lift, Missy tricks the Master into dancing with her. She tells her past self that she enjoyed her time as him, however she pulls out a knife and fatally stabs him, forcing his next regeneration, though she makes the wound "precise" so that the Master will have enough time to reach his TARDIS before regenerating.

Gradually dying, the Master compliments her, glad they haven't lost their touch. Missy tells her proud past self that he deserved nothing less than her best. After helping him into the elevator, Missy announces she will return to help the Doctor, turning to walk away as her predecessor shouts at her to not go. Missy tells her past self that this is where all the scheming, killing and egomania has led them: standing with the Doctor.

Unable to accept that his future self will side with the Doctor, the Master draws and fires his laser screwdriver at full blast, causing Missy to collapse on the ground, fatally wounded. He claims the strike has disabled her regeneration, commenting that it is the perfect ending, with them both shooting themselves in the back. They both laugh as the Master descends in the lift and Missy seemingly dies.

An initial wave of Cybermen arrive, but using Nardole's tricks with the explosives, they are able to make the humans appear more powerful, forcing the Cybermen to retreat and develop a new plan, giving the humans more time. Back at the house, and against Nardole's protests, the Doctor downloads the plans for the floor into his sonic screwdriver and sends him to help evacuate the children, intending to stay alone to fight the Cybermen. Nardole resists, having deduced the Doctor is going to commit suicide by detonating the entire floor in a last-ditch attempt to destroy as many Cybermen as possible. The pair argue over who really should die, Nardole reasoning he can't, given how he was before meeting the Doctor even though the Doctor tries to reason that he should stay as he is already dying. The Doctor eventually convinces Nardole that helping the children will be his penance for the crimes he committed before they met, as he is the stronger of the pair. Nardole jokes he will name a farm after him. Bill also insists on staying with the Doctor despite Nardole trying to tell her otherwise. As he leaves with the humans, Nardole admits that he will never be able to find the words for Bill and the Doctor's sacrifice.

With all the humans evacuated, the Doctor and Bill prepare for a last stand, each deciding to charge into opposite ends of the forest. Bill says one last goodbye to the Doctor, even joking briefly about her sexuality, assuring him she had still retained her humanity. They face the oncoming wave. The Doctor ignites several of the Cybermen, listing the numerous times he has defeated them while doing so. However, he is inevitably surrounded and receives a full strike from one Cyberman's laser beam. He declares he is the Doctor but the Cybermen retort they have no need for a doctor anymore, firing at him again. Falling to his knees, he prepares to ignite the floor but is struck again, the blast proving fatal enough that his body attempts to regenerate. Refusing to give in, he holds it back and ignites all the pipes below the floor, engulfing it all in a wave of destruction, destroying all the Cybermen.

Above on floor 0502, Nardole waits outside of one of the lifts, hoping the Doctor and Bill will return, however, Alit convinces him to move on and focus on living with them now, mentioning that Hazran has a crush on him to which Nardole smiles and retorts 'Well she's only human...'

Back downstairs, the floor is now a wasteland scattered with destroyed Cybermen. Bill, barely functioning but with her personality mostly restored, finds the Doctor severely wounded. She mourns over the Doctor's body but suddenly finds herself out of the Cyberman suit, seemingly human. She looks up and sees Heather, emerging from a nearby puddle. To prove to Bill that she isn't dead, she and Heather share a passionate kiss, when Heather reveals she converted Bill to a form of being like her. At Bill's request, they take the Doctor's body to his TARDIS, and Heather, as the Pilot, sets the controls for the TARDIS heading to a new location, while offering Bill the choice to return to her old life or to live out a new one with her, travelling the universe. Before leaving, Bill sheds a tear on the Doctor, but does not wipe it away, saying "Where there's tears, there's hope." She walks over to Heather and the reunited lovers walk out of the TARDIS into space, off to travel the stars.

The Doctor's wounds heal as he dreams of Bill and Nardole, yelling for him. He then dreams Rose Tyler, Martha Jones, Captain Jack Harkness, Donna Noble, Madame Vastra, Jenny Flint, Sarah Jane Smith, Amy Pond, Clara Oswald and River Song calling out his name. Twitching, the Doctor then dreams saying his name and he awakes, gasping for air. Seeing that he's begun regenerating, a confused Doctor mumbles some of the last words of his other incarnations. Yelling "No!" with all his might, the Doctor suppresses the complete regeneration. "I can't keep on being somebody else" the Doctor cries out as the TARDIS lands.

He tells his TARDIS that it doesn't matter where it's taken him; he won't listen to whatever kind of lesson that it's trying to teach him. The Doctor steps outside into an arctic landscape. Out in the snow, the Doctor resists the process screaming and shoves his fists into the snow, again stating he will not change.

Suddenly, in the distance hears a voice stating the same words of not changing, finding the idea ridiculous. The Doctor calls out, asking for the person to identify himself. The stranger asks for the Doctor's identity, which he confirms. The stranger replies that while the Doctor may be a Doctor, he is "the Doctor. The original, you might say". Much to the Doctor's shock and surprise, the stranger steps forth to reveal himself as his first incarnation...

Cast

 * The Doctor - Peter Capaldi
 * Bill - Pearl Mackie
 * Nardole - Matt Lucas
 * - Michelle Gomez
 * - John Simm
 * Hazran - Samantha Spiro
 * Alit - Briana Shann
 * Gazron - Rosie Boore
 * Rexhill - Simon Coombs
 * Heather - Stephanie Hyam
 * Voice of the Cybermen - Nicholas Briggs
 * The Doctor - David Bradley

Uncredited

 * Bill (as a Cyberman) - Liam Carey

Culture

 * Nardole shouts "Remember the Alamo" when getting the farmers to work.
 * When the Doctor hands Alit an apple, he refers to it as "tempting", a reference to Humanity's first sin according to the Bible.

Cybermen

 * The expedition to Floor 0507 are used as scarecrows.
 * The original Mondasian Cybermen can electrocute people by hugging them tight, and shoot death rays via their head lamps on their emotional inhibitor.
 * Nardole tells the farmers about Operation Exodus.

Technology

 * The Doctor changes the encoding in the Cybermen's system from reading one heart life forms to reading two hearts.
 * The Doctor says that parallel evolution is the reason for various civilisations evolving Cybermen.
 * Missy says Bill is doomed to live as a bio-mechanic psycho-zombie.
 * The Doctor mentions sewage and smartphones as inevitable.
 * The Doctor says the internet and cyberspace are a result of people + technology - humanity.
 * The Doctor says it took the Cybermen a while to update the net to track two-hearts instead of one-hearts.
 * The Master and Missy use their laser screwdriver and sonic umbrella, respectively.
 * The Doctor can use his sonic screwdriver as a microphone.
 * Nardole pilots a shuttle labelled SL-16.
 * Nardole uses a computer.
 * Missy carries a dematerialisation circuit because of a scolding she gave the Master.
 * Nardole says that under the floor of the farm there are fuel lines and fusion turbos.
 * The Doctor mentions the farm's cryogenic chamber.

Biology

 * Nardole again implies he is a cyborg.

Food and beverages

 * Missy calls the Doctor a "silly sausage".
 * The Doctor offers Alit a jelly baby.
 * Apples are used as grenades in the deception.
 * Heather mentions chips.
 * Bill mentions tea.

People

 * Bill asks the Doctor if her tear is engine oil.
 * Heather the oil creature returns for Bill and removes her from her Cyber-suit.
 * Missy puts on lipstick.
 * Because he's internalising, Missy calls the Doctor Mister Volcano.
 * Missy calls the farmers the Waltons.
 * Nardole was once a black market dealer.
 * The Doctor uses mathematics to conclude he can't get to the TARDIS ahead of the Cybermen.
 * The Doctor mentions Donald Trump as inevitable.
 * The Doctor likens Bill's strong resisting mind to a perception filter.
 * The Master and Missy high five each other.
 * The Master and Missy dance with each other.
 * The Master practises applying eyeliner.
 * The Master calls Bill Robo-Mop.
 * Missy creates two bootstrap paradoxes; one by telling her former self to always carry a spare dematerialisation circuit, two by creating herself by killing her predecessor.

Species

 * The Doctor says that Cybermen have monkey brains.
 * Nardole says he will name a pig after the Doctor.

Locations

 * Floor 1056 has already been converted and invaded by Cybermen.
 * The Doctor remembers being knocked out in the Conversion Theatre.
 * The Doctor recalls the Master being on his way to Gallifrey the last time he saw him.
 * The Master says the hospital has been turned into the Cyber Foundries.
 * The Doctor mentions Mondas, Telos, Earth, Planet 14, Marinus, Voga, Canary Wharf and the Moon as places where he has defeated the Cybermen.
 * Floor 0507 is a solar farm.
 * The Doctor, Nardole and Bill protect a village on Floor 0507.
 * The Cybermen are seen flying past Floor 0900.
 * The Doctor says there's another solar farm on Floor 0502.

TARDIS

 * The Master drove his TARDIS too fast towards the black hole and ended up getting stuck on Floor 1056 of the colony ship. The dematerialisation circuit of the Master's TARDIS was burnt out as a result.
 * The Doctor says that his TARDIS would not be able to properly function because it is too close to the black hole at Floor 0000.

Music

 * The song heard when Missy and the Master are dancing on the rooftop is "Midnight, the Stars and You" by Al Bowlly, a song made famous by its use in Stanley Kubrick's The Shining.

Story notes

 * The final segment of the episode, where the Twelfth Doctor meets the First Doctor in the snow, was filmed only two weeks before World Enough and Time aired, as part of filming of the Christmas special. Post-production on that scene was completed in the short time left; a week before The Doctor Falls aired, Steven Moffat stated that the final version was still being worked on. The Doctor's near-regeneration outside the TARDIS had to be completed in time for World Enough and Time, a week beforehand.
 * The Doctor's mention of Marinus as a planet on which the Cybermen originated (COMIC: The World Shapers) is another rare instance of the TV series directly referencing non-televised material.
 * This episode removes any contradiction that had previously revolved around the various Cybermen origin stories, by having the Doctor call all instances parallel evolution.
 * On original broadcast on HD, a technical fault led to sound problems which rendered the dialogue inaudible for the final five minutes: from Bill leaving the TARDIS to the end credits.
 * The use of the number 507 is a nod to Russell T Davies, who often invoked the number 57 in his writings, such as in TV: Death of the Doctor, when the Eleventh Doctor claimed to Clyde Langer that he could regenerate 507 times.
 * This is the first season finale in the revived series and the only episode of Series 10 to feature no scenes on present-day Earth, though the final scene takes place on Earth in 1986.
 * When the Doctor is dreaming of his recent past companions calling him, he sees Clara Oswald. Though fans assumed it meant his memories of her were back, it was later revealed that he didn't have them back properly until the Testimony restored them as a gift before his regeneration.
 * All three season finales during Peter Capaldi's tenure as the Doctor featured Cybermen, as well as the 12th episode of every series Steven Moffat penned as showrunner.

Ratings

 * 3.75 million (UK overnight figures)
 * 5.32 million (UK final)

Filming locations

 * Caerwent, Wales - Floor 0507 farmland.

Production errors

 * After Bill blows up the barn, a cameraman is visible on the edge of the shot.
 * In the forest scenes, several pieces of camera equipment are somewhat visible, such as a dolly and a tripod.
 * When the perspective changes away from Bill as she approaches the lift, showing her as a Cyberman again the typical stomping sound of the Cybermen is absent.

Continuity

 * The expedition to Floor 507 that "Razor" talked about are being used as scarecrows. (TV: World Enough and Time)
 * The Master and Missy admit to not knowing how many regenerations the Doctor has left after his regeneration cycle was restored. Both the Doctor and Rassilon previously wondered the same thing. (TV: Kill the Moon, Hell Bent)
 * The Master mocks the Doctor about leaving Bill alone with him for ten years. (TV: World Enough and Time)
 * The Doctor recalls last seeing the Master heading to Gallifrey, deducing that the Time Lords cured his "little condition" before kicking him out. (TV: The End of Time)
 * This is likely referring to the Master's fluctuating energy state as a result of his botched resurrection, but may also refer to the drumbeat in his head. (TV: Utopia, et al.)
 * The Doctor notes the Cybermen have risen naturally from Mondas, (TV: The Tenth Planet, AUDIO: Spare Parts) Telos, (PROSE: Doctor Who and the Cybermen) Earth, (TV: Rise of the Cybermen, The Age of Steel) Planet 14 (TV: The Invasion) and Marinus. (COMIC: The World Shapers)
 * The Doctor recounts his various victories over the Cybermen on Telos, where he sealed them into their "ice tombs", (TV: The Tomb of the Cybermen) as well as his encounter with them on Voga, (TV: Revenge of the Cybermen) in Canary Wharf, (TV: Doomsday) on Planet 14, (TV: The Invasion) and the Moon. (TV: The Moonbase)
 * The Doctor reminds Bill how she remembered the truth during the reign of the Monks. (TV: The Lie of the Land)
 * Nardole reminds Bill that he is still allowed to "kick [her] arse". (TV: Extremis) Bill tells him he will have to go down to the hospital to find it then. (TV: World Enough and Time)
 * Missy is able to provide the Master with a dematerialisation circuit by telling him to always carry a spare, similar to how the Tenth Doctor told the Fifth Doctor how he could stop the TARDIS exploding. (TV: Time Crash)
 * The Doctor reiterates River's words that Nardole once spoke to him from her diary. (TV: Extremis)
 * Missy recalls when the Fourth Doctor fell to his death. (TV: Logopolis)
 * Bill chooses the TARDIS as the Doctor's final resting place. In an alternate timeline, the Eleventh Doctor was interred in the TARDIS after his death on Trenzalore. (TV: The Name of the Doctor)
 * When waking up in the TARDIS, the Doctor says "Sontarans! Perverting the course of human history!". These were the first words of the Fourth Doctor after regenerating. (TV: Robot) He previously said the same thing after waking up from being knocked out by flying objects due to air pressure. (TV: Listen)
 * As he begins regenerating, the Doctor says "I don't want to go", the same words his tenth incarnation said before regenerating. (TV: The End of Time) He also reiterates the last lines of his eleventh incarnation; "when the Doctor was me"; (TV: The Time of the Doctor) as well saying "it's starting. I'm regenerating", the words the Tenth Doctor stated before his aborted regeneration. (TV: The Stolen Earth) He also shouts "no!" repeatedly while his regenerative energy flairs up, which was what the Second Doctor said as the Time Lords sent him away to exile. (TV: The War Games)
 * Missy severely injures one of her previous incarnations. The Master previously played a part in one of his own past regenerations due to the manipulations of the Cult of the Heretic. (AUDIO: The Two Masters) He also once killed an android with his identity, and all his memories, once done with him. (AUDIO: The Oseidon Adventure)
 * The Master is killed by a woman for the third consecutive time. The first time was by Chantho (TV: Utopia) and the second time was by Lucy Saxon. (TV: Last of the Time Lords)
 * Heather mentions Bill's job of serving chips at St Luke's University. (TV: The Pilot, World Enough and Time)
 * This is the second time that Mondasian Cybermen cause the Doctor to regenerate. (TV: The Tenth Planet) Interestingly, the Twelfth Doctor ends up meeting the incarnation from said event after their respective encounters with the Cybermen. (TV: Twice Upon a Time)
 * It's once again explained that two versions of the same Time Lord meeting results in their timelines being out of sync, and so the younger version won't retain their complete memories of the encounter. (TV: The Day of the Doctor)
 * The Doctor previously said 'You may be a doctor, but I am the Doctor. The genuine article you might say' during his fourth incarnation. (TV: Robot) He also said 'The original you might say' during his first incarnation. (TV: The Five Doctors)

DVD releases
This episode was released as part of the Series 10 DVD box set on 13 November 2017.

Blu-ray releases
to be added

Digital releases
to be added