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Recap / Doctor Who S36 E6 "Extremis"

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"They read the Veritas and chose Hell."
"Something’s coming, Bill, something very big. And something possibly very, very bad. And I have the feeling that we’re going to be very busy."
The Doctor

The one where everything is a lie.

Written by Steven Moffat and directed by Daniel Nettheim, this is the start of the "Monks Trilogy", a three-part adventure continued in "The Pyramid at the End of the World" and "The Lie of the Land".

The Doctor leans upon the Vault he's been watching over. He is afraid, in despair, and desperate to hide his new vulnerability — his blindness — from the world. He has modified his sonic sunglasses to give him some means of perceiving the world around him, but right now he is focused on a message with the title Extremis...

Once Upon a Time. The Doctor was called to a planet specializing in the execution of criminals. It was shortly after River Song had died, and he was a depressed soul. But he was needed to attend to an execution only one of his kind could perform: The execution of Missy, his Arch-Enemy. Her body would be interred in a vault for 1,000 years in case anything happened, and he vowed to watch over her body during that time. A "priest" — Nardole — came on behalf of the Doctor's late wife to warn him that she wouldn't approve of what he was about to do, to remind him of what River loved about him. But soon the Doctor stood at the lever and pulled, even as Missy plead for her life, that she could be good...


The Present Day, Earth. The Doctor is approached by no less than His Holiness the Pope to come to the Vatican, to descend into the Haereticum — a secret library of blasphemy. A short, ancient text known as the Veritas is there. Those who wrote it, and who once translated it, all took their lives afterward. And it has somehow been retranslated now, with more suicides following. The Doctor must find a way to read this text, to know what it reveals that could be so terrible. It will not be easy, and not only because he is blind. Already a copy of it has been emailed to Swiss scientists. Mysterious figures are stalking him, as well as Bill and Nardole, who find one of the portals they travel by and discover an unfolding horror beyond them.

What binds and entwines these two stories of the Doctor? Death... truth... and the nature of virtue, which is only virtue in extremis.



  • Ain't Too Proud to Beg: Missy is Defiant to the End, snarking away at her captors, but then appeals for her life to the Doctor, the one person she knows will listen to a plea for mercy from her.
  • All There in the Manual:
    • Steven Moffat explained that Nardole was sent to the Library to pick up River Song's diary so it wouldn't fall into the wrong hands.
    • In the same interview, Moffat explained that the Doctor understands the Pope's Italian as well as the translator's English, and was just playing along to avoid being awkward; dialogue to that effect was written but cut from the episode for pacing reasons.
  • Anti-Regeneration: The Time Lord execution device has, as one of its features, the ability to disrupt any regeneration energy in the condemned's body.
  • Arc Words: Episode only: "Without hope, without witness, without reward."
  • Artistic License – Engineering: Computers are bad at random numbers... but to nowhere near the degree that the Reveal relies on. (And a Sufficiently Advanced Simulation good enough to plan against, in particular, would need "good" randomness to be worthwhile.)
  • Awful Truth: The Veritas reveals a truth so horrible that all who read it are driven to kill themselves: the knowledge that their world is a simulation and so are they. As the Doctor puts it, if you were aware of your own existence as a character in a video game, doomed to repeat it forever, wouldn't you want to delete yourself?
  • Badass Boast:
    • Nardole is the only being sanctioned to kick the Doctor's arse, and he'll do the same to Bill if she doesn't follow instructions given to her for her own safety.
    • The Doctor gets a very unusual but awesome Badass Boast in a series of single word answers to the executioner, compounded by the continuous background noise of the Fatality Index's search results popping up.
      The Doctor: Do me a favor. The Fatality Index. Look up "The Doctor"...
      Executioner: You have an entry, like any other sentient being.
      The Doctor: ...under cause of death.
      Executioner: [device pinging] You do seem to have an impressive number of fatalities connected to you. [device keeps counting] A truly remarkable record. [device clicks faster, the guards begin leaving] Where are you going?! He's unarmed! You are unarmed?
      The Doctor: Always.
      Executioner: [device is now emitting a high pitched whine as it counts higher] You stand alone.
      The Doctor: Often.
      Executioner: [angrily] You're the one who should be afraid.
      The Doctor: Never.
      Executioner: [results are still coming] Have a nice day, then. [hurried exit stage left]
  • Bait-and-Switch: The episode opens with a sequence which appears to be the Doctor being taken to his own execution, but he's actually the executioner and Missy is the victim.
  • Beethoven Was an Alien Spy: Apparently, Pope Benedict IX was actually a woman.
  • Being Good Sucks:
    • Missy chokes on her words while saying she'll be good if the Doctor saves her.
    • And the Doctor choosing to be good still saddles him with the duty of watching over Missy's body for 1,000 years. This means he has to take The Slow Path rather than enjoy all of space and time. While it's been established that he's used the TARDIS on occasion, before he met Bill it's likely he didn't travel anywhere but to other parts of Earth in need of help in whatever The Present Day was at the time.
  • Bizarrchitecture: The Haereticum as a security measure.
    Cardinal Angelo: Please, stay close to me. The layout is designed to confuse the uninitiated.
    The Doctor: Sort of like religion, really.
  • Blind Mistake: After the Doctor temporarily restores his eyesight with a gadget, his vision is extremely blurry, so when he sees a Monk approaching him, due to its red robes he assumes it to be Cardinal Angelo, who was vanished by the Monks several minutes earlier.
  • Brits Love Tea: Bill brings home a girlfriend. Moira says not to do anything she wouldn't do. Instead of a Gilligan Cut to lesbian snogging, we have Bill pouring Penny a cup of tea.
  • The Bus Came Back: Missy returns, marking her first appearance since "The Witch's Familiar" way back at the top of Series 9.
  • Call-Back:
    • Missy notes to the Doctor that she knows that he'd been enjoying "Domestic bliss on Darillium, that's the word among the Daleks." From there, Nardole reads to the Doctor from River Song's diary to remind him of his best self and thus discourage him from executing Missy.
    • In the previous episode, the Doctor noted that "The Universe shows its true face when it asks for help. We show ours by how we respond." It turns out that long ago, when Missy plead for her life, the Doctor responded by letting her live. In addition, the Sim-Doctor responds to the risky request of the Vatican to read the Veritas, and in his "dying" moments asks for help from the real Doctor, who knows that he must save his world from the Monks, though he feels scared and helpless. Now, he is asking Missy for help. How will she respond?
  • Captain Obvious:
    • Nardole takes up this role intentionally so the Doctor knows what's going on without letting anyone in on the fact that he's blind.
    • The Doctor himself, once or twice, whenever he belatedly realizes something everyone else saw a while ago.
  • Clap Your Hands If You Believe: In the climax, knowing both that he is just a computer construct of a real person and that the Monks will soon destroy him for knowing too much, the Sim-Doctor realizes "But right now... belief is all I am. I am the Doctor." With the realization that he can be the Doctor just by never giving up — even if he isn't "real" — he uses his sonic sunglasses to send a message to the real Doctor's sonic sunglasses, warning him of the threat to Earth. Thus, he exploits this trope before he is destroyed.
  • Cat Scare: Bill shrieks on finding there's someone in the cage.
  • Chick Magnet: Nardole says, "You old dog" on catching sight of the painting of Pope Benedict IX, a friend of the Doctor's.
  • Cliffhanger: The Doctor knows the Monks are going to invade Earth and is already formulating a plan to fight them, but he is still blind and afraid — and seems ready to let Missy out of the Vault to call upon her help.
  • Clothing Reflects Personality: The Doctor's coat in the Missy scenes is noticeably worn. As these scenes take place in the wake of the death of River Song, it suggests that his grief caused him to neglect caring for himself and his appearance.
  • Continuity Nod:
    • The Vatican comes seeking the Doctor's help on a personal recommendation from Pope Benedict IX, written in 1045, similar to Queen Elizabeth I's "credentials" from "The Day of the Doctor".
    • Penny asks Bill if she was going to move out of her foster mum's flat, and Bill responds that yes, she was, but it didn't work out, and that she plans to try again later.
    • Angelo comments that the Doctor is "more in need of confession" than anyone. He then says the Doctor refused the offer because "It would take too much time."
    • After previously expressing extreme distaste at the idea of turning good, Missy swallows back her visible revulsion at the idea as she offers to learn how to be good if the Doctor will only save her life.
    • Way back in "Last of the Time Lords", the Doctor was also faced with the prospect of guarding the Master, and brought up the possibility of having to stop travelling to do so.
    • The door to the Haereticum is a large portrait of Pope Benedict IX, who was actually a woman — similar to how the door to the Undergallery is a portrait of the Tenth Doctor and Queen Elizabeth I.
    • The way the Monks turn the lights in the Haereticum back on is similar to the ability of the Weeping Angels to switch lights off.
    • This isn't the first time the Doctor has gotten people to back off by telling them to look him up. Apropos, as we also get a nod to "Forest of the Dead" with Nardole showing up with River's diary.
    • This is not the first time the Doctor's found himself in the Oval Office sitting at the President's desk.
    • This also isn't the first time the Doctor has been asked to deal with the remains of his "best enemy" after execution.
    • Aliens creating an Earth simulation to practice for an invasion? It didn't work too well for the Kraals, but the Monks have much better technology and their creation is much greater in scale.
    • The Sim-Doctor's reading device burns out part of his brain and compromises his future health/ability to regenerate. Add to that the process of donning it, attaching sensors to his forehead and all, and it's painfully similar to the many, many Doctors giving up their lives in "Heaven Sent" via the hotwired teleporter.
    • The present day storyline turns out to be a simulation rather than reality, but it still has tangible effects on the real world. In "Last Christmas", everything but the final minutes of the episode was a dream the Doctor and Clara were having, the work of the Dream Crabs trying to consume their brains. But the process of escaping the shared dream also allowed them to reconcile after the events of "Death in Heaven", and once awake they were happily reunited in the real world.
    • Bill asks Nardole if he feels afraid when the Doctor says to trust him. In the previous episode, the Doctor did this before leaving Bill to be electrocuted by killer zombie spacesuits.
  • Copied the Morals, Too: The simulation of Earth is so good that the simulations still have their personalities and full, uncontrolled self awareness. And the copy of the Doctor is so good that he's determined to thwart the people behind the simulation, and manages to send a message about everything to his real-world counterpart.
  • Dead-Hand Shot: The last translator gets one after he shoots himself in the Haereticum, his hand holding the gun he killed himself with.
  • Deadly Book: The Veritas contains undeniable proof that the reader, the world, and everyone in it are computer simulations, being run by an alien race in preparation for an invasion of Earth, a revelation so shocking that nearly everyone who reads it (except the Doctor) is Driven to Suicide.
  • Determinator: The Sim-Doctor declares that he doesn't need to be real to be the Doctor — anyone can be the Doctor so long as they never give up.
  • Do Androids Dream?: The Doctor claims that all simulations, including video game Mooks, can think and feel.
  • Do You Trust Me?:
    Bill: Does it give you the fear when [the Doctor] says trust me?
    Nardole: If I worked here, I'd cross me-self.
  • Driven to Suicide: The fate of all readers of the Veritas is to kill themselves. Why they do so is given several explanations: they think they are escaping, that they are saving the world (say by corrupting the fidelity of the simulation), or that they're seeking death out of despair.
  • Driving Question:
    • What does the Veritas reveal that drives all of its readers to suicide?
    • Who is the prisoner in the Vault, why are they imprisoned, who imprisoned them, and why is the Doctor their guard?
  • Drowning Their Sorrows: The CERN scientists, after reading the Veritas, get themselves drunk on many bottles of wine before they blow themselves up.
  • Elephant in the Living Room: Nardole says the real reason the Doctor refuses to tell Bill about his blindness is that it means acknowledging it to himself.
  • Enemy Mine: Hinted at: The Doctor mentions that, if he, Bill, and Nardole can't stop the Monks by themselves, he may be forced to let Missy out of the Vault in order to stop them.
  • "Eureka!" Moment: Facing the Monk at the end, the Sim-Doctor quotes the line about "without hope, without witness, without reward", which makes him realize that the recent events have not gone unwitnessed, because his Sunglasses have recorded everything, and that if he can get the recording to the real Doctor there is still hope.
  • Everybody Lives: An odd example, as yes, there are on screen deaths. However, they are merely simulations, and their real life counterparts are still very much alive.
  • Exact Words: The Doctor swore an oath that he would guard Missy's body for a thousand years, but he didn't mention her having to spend that time dead, or even in the Vault.
  • Eye Motifs: The Doctor is still blind after the events of "Oxygen". His simulation doppelganger is also blind, but briefly regains eyesight over the course of the episode as he and others come to "see" the truth of their world. In the end, he gets a message out to the real Doctor via the sonic sunglasses that both Doctors have modified to cope with their condition.
  • Foreshadowing:
    • At the end of the teaser the Doctor sits in front of the Vault and receives an email on his glasses. Then, as the title sequence starts the screen gets all glitchy. When the screen gets glitchy again near the end of the episode, it becomes apparent that these mark the beginning and end of a recording contained in the email.
    • When the Doctor first "sees" a Monk in the portal open in the wall, his sunglasses can't register its species, gender, or age, unlike everyone else seen so far in the episode.
    • When the Doctor is confronted by the Monks in the Haereticum, they taunt him by saying "This is a game."
    • In that same scene, when the Doctor switches off the lights to escape, a Monk is able to turn them back on moments later.
    • Throughout the episode, there are a series of glitches that one might mistake as bad feed from a cable or satellite hook up. It's actually Stylistic Suck meant to foreshadow the simulated environment.
  • Fade to White: Used for a Sound-Only Death — the companions flee back to the White Void Room just as the CERN scientists blow themselves up.
  • Fake Kill Scare: The Doctor pulls the lever on Missy, who collapses to the ground... only to reveal that the Doctor sabotaged the device.
  • Flatline: After the translator shoots himself, the Doctor watches his heartrate readings drop to nil.
  • Framing Device: The frame is the real Doctor watching his simulant's memory print of the last several hours of the most recent simulation while sitting in front of the Vault.
  • Freeze-Frame Bonus: When the Doctor's companions read the email-client screen on the translator's laptop, beyond the top-screen mail from CERN, it's filled with references to the world being not what they thought it was and requests to pray for them. Some of the French ones say things like "Pray for us all", "The world is not what we think" and "We've all been tricked by the devil"...
  • A Glitch in the Matrix:
    • The Veritas reveals that the "world" is a simulation. To prove it, readers are invited to think of a series of random numbers: everybody will always come up with the same sequence. As the Doctor notes, "computers aren't very good with random numbers."
    • invokedWord of God is that the President having dark hair (where the real President at the time of filming was blond) is also a flaw in the simulation.
  • Glasses Pull: Nardole when he decides to drop the comic relief act and tell Bill to do what she's told.
  • Godzilla Threshold: The Monks pose such a threat to Earth that the Doctor is willing to let Missy out of the Vault to help as the episode ends.
  • Goggles Do Something Unusual: The Doctor has been using the sonic sunglasses to compensate somewhat for his blindness, as they can psychically transmit information into his brain. They give him an outline of the area within his field of view, and a HUD showing people's species, gender, age and heart rate. However, they can't show lighting or help him read things and identify people within his field of view.
  • Go Mad from the Revelation: Those who read the Veritas and learn its "truths" end up Driven to Suicide. Turns out the book reveals the world is a simulation created by the Monks to help them conquer the Earth.
  • Gone Horribly Right: The Monks create the simulation to be as realistic as possible. The realism means the simulated Doctor has both the technology and the will to warn the real Doctor about the threat they pose.
  • Gondor Calls for Aid: An unusual example, as the Doctor receives a summons for help from himself, or at least a simulacrum that was just a little too well made.
    Simulant Doctor: I'm doing what everybody does when the world is in danger. I'm calling the Doctor.
  • Great Big Library of Everything: The Haereticum is massive, holding at least a thousand years' worth of texts the Vatican has deemed too dangerous to be left to the public.
  • Heroic Sacrifice: What everyone who's been Driven to Suicide is actually doing; they're stopping the Monks from collecting data on Earth by killing themselves.
  • Hidden Badass: After Nardole's Badass Boast about how seriously he takes instructions and his willingness to kick the arse of even the Doctor, and all in a serious-no-nonsense tone while acting as a Human Shield for Bill, Bill asks, "Are you secretly a badass?" He says it's not a secret.
  • Hiding the Handicap: In both the real and sim worlds, Nardole is the only one who knows the Doctor is still blind, and the latter would like to keep it that way. Sim-Nardole claims he's doing this to deny and thus avoid dealing with the reality of his condition, but the Doctor does have another justification — he doesn't want his enemies to know he's vulnerable. With the modifications he's made to the sonic sunglasses, he is dealing with his disability to an extent, but it can only go so far and it's going to make life and saving others' lives harder until he regenerates.
  • His Story Repeats Itself: At least a century after the events of "Death in Heaven" from the Doctor's perspective, he once again has the opportunity to kill a helpless Missy. Others want him to do so, and he knows that she will only cause more trouble if he shows mercy. But where he was ready to do so in "Death in Heaven" and sadly told Missy that she'd won because he was lowering himself to her level, and was only stopped because the Cyber-Brigadier shot first (of course, either way she would have escaped via Vortex manipulator), this time he chooses to let her live and accepts the responsibility of watching over her, knowing that this is the choice of a good man.
  • Historical In-Joke: There were persistent rumors of a female Pope, a Sweet Polly Oliver called Pope Joan who reigned during the Middle Ages. Most modern historians doubt the tale. It wasn't Benedict IX however, though his reign was pretty scandalous in its own right (likely why the Doctor has such fond memories).
  • Honour Before Reason: The Doctor cannot bring himself to execute Missy but will hold to his Exact Words, so now he is (mostly) stuck on The Slow Path guarding the Vault she's imprisoned in. If he slew her, he still would have had to stand vigil in case her corpse came back to life, but instead she's alive and well all along, could escape at any time to wreak grisly havoc, and will eventually be freed. And he gains absolutely nothing for his choice, but as River Song's diary reminds him, to truly be good requires total selflessness.
  • Hub Level: The Monks' simulator appears at first glance to be one, with portals to the Vatican, the Pentagon, CERN, the White House...
  • Humanoid Abomination: The Monks are an extension of a horrible thing from beyond the reality the sim-characters inhabit. When one talks its words don't correspond to its mouth movements at all, as though it understands that you open your mouth to speak but hasn't bothered to learn why.
  • Hurting Hero: The Doctor is in despair at the end of this story: He knows that an Alien Invasion of Earth by a cunning new enemy is imminent, but he is blind and desperate to hide his vulnerability, his technology can only go so far to aid him, one of his companions has never faced a danger of this scope and scale, and his only hope for additional help is to let one of the most dangerous people in the universe out of the Vault.
  • Hypocrite: Moira has strict rules against Bill bringing men home, but doesn't stick with a boyfriend long enough for Bill to remember their names.
  • Hypocritical Humor: Nardole claims to be a badass, then squeals on seeing a dead body.
  • Incredibly Obvious Bomb: It is once Bill looks under the tables. Then she realises what the countdown on the nearby computer screen is about.
  • Innocently Insensitive: The Pope had absolutely no clue how absurdly à propos his blessing was...
    Cardinal Angelo: [translating] May God illuminate your path.
    The Doctor: He could certainly give it a go.
  • Impairment Shot: There's a kind of disimpairment shot showing the Doctor's temporary eyesight fix slowly beginning to work, and later a straight use of the trope when his eyesight begins to slip away again.
  • In the Hood: Nardole pretends to be a priest under a cowl that hangs over his face so he can deliver River's message.
  • Invisible President: The simulated President's body is seen, but only from behind.
  • Joker Immunity: As one of the show's Top 3 villains (the others being the Daleks and the Cybermen) and the only one who can work solo, Missy yet again escapes the jaws of death. Since this is so inevitable, the episode builds suspense over how that will happen: Either the Doctor goes through with it but her body proves hardy enough to revive during its internment in the Vault, or he spares her and she's just locked up for 1,000 years. Turns out to be the latter!
  • Kneel Before Zod: Missy has to kneel for her execution.
  • Knight of Cerebus: Two. Until "Oxygen", the adventures of Series 10 were relatively light — especially for the Twelfth Doctor — and even "Oxygen" continued the trend of one-off antagonists, "villains" who weren't actually evil, and happy endings for the rescued. He's on good terms with his companions, one of whom is primarily comic relief, and sure of his identity with no major anxieties plaguing him. But "Oxygen" rendered the Doctor blind as a consequence of his recklessly risking himself and his companions' lives, and now two examples of this trope are introduced. Steven Moffat says that this dramatic shift was intentional, as Bill wouldn't have stayed a companion for long if she'd immediately been plunged into stories like "Oxygen" and this. The knights are the Monks, who appear to be walking corpses and whose purely Evil Plan first involves making a simulation to run through all possible ways they could be stopped, of which the real Doctor only knows they're coming thanks to the Heroic Sacrifice of his sim-counterpart, but also knows that they're one of the worst threats he and humanity may ever face; and Missy, the Twelfth Doctor's Arch-Enemy, is back. Right now she's safely sealed in the Vault, but the Doctor needs help to face the Monks, especially now that he's blind...
  • Madwoman in the Attic: This episode confirms that Missy — an evil, insane Time Lady — is the prisoner of the Vault.
  • The Masquerade Will Kill Your Dating Life: Sim-Bill's attempt at a normal date is interrupted by the Pope inexplicably appearing from her bedroom in a state of agitation.
  • Meanwhile, in the Future…: The action shifts between Missy's execution, which takes place not long after "The Husbands of River Song", and the simulation — and the Doctor guarding the Vault in the real world — in The Present Day, which is at least several decades later in the Doctor and Nardole's timelines.
  • Moment Killer: The Pope is naturally good at this. All he has to do is walk into the room, say something in Italian, and then exit and the romantic mood is gone.
  • Morality Chain: Nardole's promise to look after the Doctor for River Song involves being this, as he arrives just in time to urge the Doctor not to execute a helpless, if evil, woman. It helps that River is now a Morality Chain Beyond the Grave herself.
  • Morality Chain Beyond the Grave: River Song is now this to the Doctor, as Nardole points out when he arrives at the execution. He reads to the Doctor from her diary to remind him of his best self and convince him not to execute Missy, and it works.
  • More Expendable Than You: The Doctor tells Nardole to walk in front of Bill when looking for the crazed man with a gun. Nardole snarks accordingly, but takes this responsibility entirely seriously.
  • Motifs: Series 10-specific:
    • Hidden threats: The Monks first appear in portals that turn up in walls (beings specifically hidden in or even being walls also turn up in "Smile" and "Knock Knock").
    • Unusual books: The Veritas and River Song's diary, both of which are crucial to the plot(s).
    • Imprisonment/release: Missy is the prisoner of the Vault; the Doctor might have to release her.
    • Promises: The nature of the Doctor's mysterious vow (to watch over Missy, who is in the Vault, for 1,000 years) is revealed at last, and alongside that it turns out that Nardole serving as the Doctor's companion stems from a promise he made to River Song.
    • Truth: Missy says that she has to speak the truth "Without hope, without witness, without reward" as the Doctor prepares to "execute" her. The Veritas reveals the true nature and purpose of the simulated world to its residents, and those who learn it are trying to spread it to save the real world. The Sim-Doctor (and his real world counterpart) refuses to reveal the truth of his blindness to others, with Sim-Nardole claiming it's because he can't bear to face that reality (i.e. admit he's vulnerable). In the real world, the Doctor is telling the truth to Missy — that he is scared and in need of help.
    • "Villains" who aren't actually evil: Those who share the Veritas, which inevitably causes its readers to kill themselves, are actually trying to save the real Earth from the Monks by denying them the information they need to successfully invade and conquer it.
    • Exploitation: Residents of the simulated Earth are unknowing creations/tools of the Monks who are observing them to figure out how to invade the real Earth. Those who realize they and their world are not real, and why they were created, rebel in hopes of protecting their real-world counterparts.
    • The value of each individual life: The Doctor spares Missy's life simply because it's the right thing to do.
  • Mundane Solution: In order to read the Veritas, the Doctor uses a futuristic gadget to restore his eyesight for a few minutes. It's painful, costs some health from his future self, for most of the time his vision's too blurred to read, and he barely gets past the title before it wears off. He finally manages to "read" the book by using a laptop with a text-to-speech function.
  • Mythology Gag:
    • The Vatican maintaining a library of "forbidden knowledge" is nothing new to the Doctor Who mythos; several of the Doctor Who New Adventures and Doctor Who Missing Adventures featured or contained references to such a library, called the Library of St. John the Beheaded. All-Consuming Fire, the main novel that features it, and has a plot driven by one of the forbidden documents getting loose in the world, also begins with the Pope making a personal appearance to request the heroes' aid.
    • The 1996 TV movie was kicked off by the Master being executed by experts at killing (in that case, Daleks) and left to be guarded by the Doctor.
  • Nested Story Reveal: The majority of the episode takes place in a computer simulation created by the Monks in preparation for invading Earth. The real Doctor, Bill, and Nardole were never involved in the story, and it turns out we've been watching simulated versions of them for most of the episode. One of the Monks reveals that they've done the same simulation many times, and implies that they all end with the Doctor's death. However, this time the simulated Doctor is able to send a message to his real self to warn him due to the Monks making the technology within the simulation "too good".
  • Never Found the Body: Cardinal Angelo informs the Doctor that all of the translators who worked on the Veritas killed themselves — except one, whose body was never found. The Church assumed he'd committed suicide like the others, but the Doctor points out that since they haven't found the body, he may not be dead. They find him in the Haereticum, just after he'd sent the translation of the Veritas to the world's most important institutions.
  • Never Trust a Trailer: Besides all promotional materials hiding the Nested Story Reveal, the Doctor's warning to Bill that "something very big. And something possibly very, very bad" is coming and the question "How can I save them when I'm lost in the dark?" were used, suggesting he said them as part of the main action. Those lines are from the Cliffhanger leading into the next episode, and he doesn't know how he can save them yet.
  • Nice Job Fixing It, Villain:
    • The Monks made their simulation of Earth extremely realistic. So realistic, in fact, that as the simulated Doctor points out, the technology within is "too good": simulated software (such as that on his simulated sonic glasses) is still real software, enabling him to send a warning email to the real Doctor.
      • The Doctor even alludes to Zawinski's Law by pointing out to the Monks that even "jumped-up little subroutines" can send email.
    • To say nothing of their simulation of the Doctor being too good for the villains' own good. Realizing who and what he is, the simulacrum Doctor immediately sets out to contact the real deal.
  • Non-Answer: The Doctor's response to Bill inquiring why he's wearing his sunglasses indoors.
    Bill: Dark enough for you?
    The Doctor: In darkness we are revealed.
  • Noodle Incident: The Doctor's night with Pope Benedict IX (who was apparently female and could do naughty things with castanets) in 1045.
  • No Kill like Overkill: The Time Lord execution device is designed to simultaneously stop both hearts and all three brainstems, and to disrupt regeneration energy in the victim's body. Given what's been established about Time Lord physiology, this is likely justified. And even after that the body has to be kept under lock and key for a thousand years, in case it tries anything.
  • Oblivious Guilt Slinging: Closet lesbian Penny is already nervous about going on a Not a Date with Bill; having the Pope barge into the room shouting in Italian is enough to make her flee.
  • Oh, Crap!: The Doctor gives one to the executioners when he asks the head executioner to look him up on the Fatality Index, and they discover he has a very long list of fatalities at his hands, even though he's unarmed and alone. In fact, he's virtually a cause of death! Eventually, they all flee.
  • One-Word Title: "Extremis", from the Latin phrase in extremis, which, according to Merriam-Webster, means "in extreme circumstances" or "at the point of death."
  • Please, I Will Do Anything!: Missy says this to the Doctor as he prepares to pull the switch, claiming she'll even learn how to be good.
  • Plot Parallel: Both the real Doctor and the Sim-Doctor find themselves tested in extremis, at the point of death. In the real Doctor's case, it's Missy's death; all he has to do is pull that switch and let her fry. In the Sim-Doctor's case, having realized he is not real, he will soon have to "die" either by the Monks or his own hand. Both face the prospect of doing the right thing — spare Missy, find a way to warn the real Doctor — "Without hope, without witness, without reward." Both of them choose to do what is right.
  • Portal Network: Or so it appears when Bill and Nardole step into the light and find themselves emerging on a restricted floor on the Pentagon. It's only later that Nardole realises they are actually holographic projectors.
  • The Power of Friendship: One reason the Doctor cannot bring himself to kill Missy for good. They were friends once, and more than any other incarnation of the Master, Missy wants to be his friend again.
  • Pre-Climax Climax: The Doctor invokes it, telling Bill to hook up with Penny immediately because there's an alien invasion on the way and they're going to be very busy tomorrow.
  • Previously on…: Those who missed last week's episode are filled in on the Doctor's blindness.
  • Prolonged Prologue: Serves as this to "The Pyramid at the End of the World" and "The Lie of the Land".
  • The Promise:
    • The Doctor has promised to look after Missy's body for 1,000 years.
    • Nardole is looking after the Doctor because he promised River Song that he would.
  • Random Number God: In a way. Every time a simulant rerolls a number, it comes out as the one number they didn't want: the exact same one as everyone else. In fact it doesn't seem to use a real random number generator at all, just a set sequence (which is written down in the Veritas as a quick test).
  • Red Herring:
    • The Twelfth Doctor sacrifices a part of his future selves' health, risking his ability to regenerate ever again. Turns out, it was just a simulation.
    • One of the translators exclaims he "sent it", hinting at the mail seen at the beginning. Turns out, he sent the translation of the Veritas to several major institutions, including the White House and the CERN.
  • Red Is Violent: The deadly, cadaverous Monks wear red robes.
  • Re Imagining The Artifact: The Doctors Sonic Sunglasses from the previous season are now needed to help him see in spite of his blindness.
  • The Reveal: Missy is the person in the Vault, and the Doctor promised to watch her after he saved her from execution.
  • Sadistic Choice: As in "Death in Heaven", the Doctor is faced with either executing a helpless Missy and failing to be his best self, or letting one of the most dangerous people in the universe live when he has no reason to trust her pleas that she can learn to be good. While he was ready to pull the trigger in that story, he really didn't want to, and this time he decides to let her live. While she will be under lock and key for 1,000 years, at the end of that time she will be freed.
  • Save the Villain: The Doctor deciding to save Missy from execution is how this whole Story Arc began.
  • Sealed Evil in a Can: Missy, one of the most dangerous criminals in the space-time continuum, is in the midst of a 1,000-year imprisonment in the Vault. Even if the Doctor had executed her she still would have qualified as this because, as a Time Lord, her body might yet revive at some point and thus needed to be interred in a safe place.
  • Schmuck Bait: Bill and Nardole agree that walking into the glowing light doorway would be a really bad idea. As they are companions of the Doctor, they do it anyway.
  • Series Continuity Error: The Doctor and Nardole teamed up in the wake of Missy's "execution", which is implied to have been shortly after River Song's death — so why doesn't Nardole, who hates the Doctor being away from the Vault, bring this up at all in "The Return of Doctor Mysterio"? Why is the Doctor's grief over River's death so fresh in that story if he'd already been guarding the Vault for several decades?
  • Shackle Seat Trap: A self-restraining version to prevent anyone reading Veritas from killing themselves (but how do you turn the pages?)
  • Shoot Out the Lock: The translator breaks into the cage this way.
  • Shout-Out:
    • Pope Benedict IX being a woman is one to the legend of Pope Joan.
    • To Tom Lehrer — one of the scientists in the mass suicide at CERN proclaims "We Will All Go Together When We Go".
    • The simulated Doctor compares those who read the Veritas and learning about the simulation to "Super Mario figuring out what's going on, deleting himself from the game because he's sick of dying."
    • Similarly, Nardole name-drops Grand Theft Auto when he realises the entire world is just a videogame-style simulation.
    • Nardole also compares the simulation to the holodeck in Star Trek.
    • The themes of Vatican secrets, CERN, and world-shaking revelations smacks a great deal of the various works of Dan Brown.
    • In an interview, Moffat mentioned The Name of the Rose as an inspiration, especially with the labyrinthine library.
    • Bill exclaims "Harry Potter!" when she sees the Haereticum.
  • Snipe Hunt: The Doctor sends his companions to see if the priest who just shot himself is still alive and needs help. As the Doctor wouldn't send them to find a crazed gunman in the dark, Nardole realises the Doctor is trying to get rid of them so he can read the book. Just to drive the point home, as the Doctor asserts that they don't know that the priest is dead, we get a POV shot of his sonic sunglasses telling him that yes, the priest is definitely dead.
  • Spare Body Parts: Not only do Time Lords have two hearts, they also have three brainstems.
  • Starts with a Suicide: The main plot starts with many suicides, thanks to the Veritas being retranslated.
  • Stealth Hi/Bye: When he gets cornered by the Monks in the cage where the Veritas is kept, the Doctor switches out the lights. When the lights come back on, he's vanished with the laptop with a translation of the Veritas.
  • Stepford Smiler: The CERN scientist who was leading the group suicide, and at least half of his friends, are smiling and laughing while the bomb ticks down.
  • Suicide Is Shameful: Cardinal Angelo notes that all the people who are known to have read the Veritas were devout Catholics who were aware that suicide would be considered a mortal sin... and they still chose Hell after reading the book (because they learn that they're only computer sprites and therefore ending their own existence won't send them to Hell, Heaven, or anywhere else).
  • Sunglasses at Night: Bill at one point asks the Doctor why he's wearing his sonic sunglasses indoors, to which he gives her a non-answer. The audience, of course, knows what he's not telling her...
  • Take Over the World: The intention of the Monks, but before they can do so, as Sim-Doctor explains to Sim-Bill, they must completely understand it — and its residents — first.
  • Take That, Audience!: Many fans complained about the Doctor's sonic sunglasses in Series 9. The Doctor enhancing them to deal with his blindness has been interpreted as — at least in part — a take that at those viewers, as he now has to wear them constantly as his most important gadget!
  • Temporary Blindness: The Doctor is still blind following the events of "Oxygen", apparently has no means of curing it, and he's determined to keep it a secret — even from Bill, possibly to spare her guilt (since he lost his sight by way of saving her life). It still counts as temporary for the Doctor because he will be able to see again at some point in the future, which at the latest will be when he regenerates.
  • Tempting Fate: Bill notes that at least one person read Veritas and didn't kill themselves. Cue gunshot.
  • These Are Things Man Was Not Meant to Know: The contents of the Veritas — it reveals that the world is a simulation by a group of aliens who want to invade Earth, and thus that no one who is in it is real.
  • Title Drop: "Extremis" is used as a code phrase several times, including by the Pope; Nardole, when he's telling the Doctor that he promised River he'd look after him; the CERN scientist who Bill and Nardole talk to, who, along with his colleagues, is getting drunk before committing suicide as a group after reading the Veritas and says "In vino veritas"; and the Doctor himself, when the simulated version sends the real deal the emailed memory-print. In all cases, it's used to indicate the severity of the situation.
  • To Be Lawful or Good: The Doctor could be lawful and execute Missy, or good and let her live. He chooses the latter and uses Exact Words to keep to his oath regardless.
  • Tomato in the Mirror: The Nardole, Bill and Doctor we've been following through the episode realise that they're simulants in the Monks' computer. Sim-Nardole and Sim-Bill are quickly disposed of, but Sim-Doctor manages to get off a warning to the Doctor proper.
  • Tome of Eldritch Lore: The Veritas appears to be one of these; an ancient tome that is locked away in a secret library reserved for heresy that causes whose who read it to commit suicide. In truth, the Veritas is a mundane book with an Awful Truth.
  • Two Lines, No Waiting: The bulk of the episode alternates between the execution of Missy in the past and the Monks' simulation in the present.
  • Villains Want Mercy: Whenever the Doctor looks like he's about to execute her, Missy starts pleading for her life.
  • Virtual-Reality Interrogation: The Monks' simulation does this to the entire Earth, in preparation for their planned invasion.
  • Visual Pun: "The bomb under a table" (the simulated CERN scientists' chosen means of suicide) is also a classical example of a suspense scene coined by Hitchcock.
  • What Happened to the Mouse?: While Missy brings up River Song upon meeting the Doctor again, even offering condolences when she realizes River is dead, she never brings up — in this or any other Series 10 episode — Clara Oswald, even though she was personally responsible for bringing the Doctor and Clara together in the first place, possibly as a ploy to create the Hybrid and corrupt the Doctor. Although she knows that the Doctor and River were living together (apparently from the Daleks!), she doesn't seem concerned as to what became of Clara to allow that to happen. Moreover, the Doctor never expresses any resentment towards Missy over her manipulation of his and Clara's relationship. Granted, at this point the Doctor doesn't even remember her, but still.
  • What Measure Is a Non-Human?: The episode explores this concept. All of the characters are revealed to be part of the simulation, including the Doctor, Bill, and Nardole. The Doctor explains that even though they are part of a program and are shadow copies of the originals, they are so real that they have self-awareness, being capable of the same thoughts and decisions as their real counterparts. The Sim-Doctor manages to use this to his advantage and email a recording of the Monk's Evil Plan to the Doctor in the real world.
    Sim-Doctor: "But right now... belief is all I am. I am the Doctor."
  • What You Are in the Dark: River Song's diary, and from there Missy, bring this concept up to the Doctor: That "Virtue is only virtue in extremis", that a person's true nature is revealed when they face the prospect of being "Without hope, without witness, without reward."

"How can I save them when I'm lost to the dark?"