The Pilot (TV story)

 was the first episode of the tenth series of Doctor Who produced by BBC Wales. It introduced the Twelfth Doctor's new companion, Bill Potts.

According to Steven Moffat in a video introduction, "series 10 sort of begins the show again. [The Pilot] introduces everything you need to know about Doctor Who, and tips you into the universe". Indeed, through Bill's eyes now, new viewers are introduced again to the character of the Doctor, his TARDIS, his enemies the Daleks, and his versatile tool, the sonic screwdriver, much like they did through Rose Tyler in series 1's 2005 "pilot", Rose, or through Ian and Barbara in the original 1963 introduction, "An Unearthly Child". Much like Rose, The Pilot follows Bill around in every scene.

This was also the first on-screen depiction of Movellans since their debut in Destiny of the Daleks. The episode introduces St Luke's University, where the Doctor apparently has been lecturing for over fifty years, and begins a plot thread surrounding what he and Nardole are hiding in a vault beneath the campus. This bears some similarity to the era of the Third Doctor, who was likewise restricted in his travels and held a job as the scientific adviser of UNIT.

Some things were different with Bill as a companion; she was panicky when first travelling in the TARDIS, and took a long time to figure out that it was "bigger on the inside". Continuing the unofficial theme of having the Daleks appear in each season of the Revived Series, the Doctor attempts to destroy the sentient oil with the deadliest fire in the universe, which turns out to the Daleks.

By the Doctor's own admission, he has come to believe that if he encounters some kind of alien on Earth, it is likely going to be dangerous as most of the past aliens he's encountered on Earth have been. However, in a twist, the "threat" turns out to be a misunderstanding caused by a crush.

This episode marks the first time since The Snowmen that the lights in the TARDIS have been off. However, unlike back then, ALL the lights are now able to be shut off when the Doctor hasn't been inside for a while.

Synopsis
The Twelfth Doctor — now living and teaching at St Luke's University on Earth — convinces dinner lady Bill Potts to be his private student. The Time Lord and his companion Nardole soon discover that their new friend has unwittingly made a deal with a prospective girlfriend that threatens their safety in a way that even the TARDIS can't outrun.

Plot
The episode opens with an empty university professor's office; nobody is in. The sound of mechanical whirring is heard for a while before the door opens and Nardole leads a woman called Bill Potts in; he gestures for her to take a seat at the professor's desk. A bolt falls out his arm, but he discretely kicks it away before Bill can notice. He leaves without a word, leaving Bill to wait for the professor to arrive.

Bill looks around the room, finding the TARDIS in a corner, with an "Out of Order" sign hanging on it. She notices a mug on the professor's desk full of the Doctor's old sonic screwdrivers, and reaches out to examine one. However, she is startled by the sound of an electric guitar playing the opening bars to Beethoven's Fifth Symphony. She coughs loudly to make her presence known, and the Doctor sticks his head round the door.

Putting his guitar away, the Doctor takes his seat and asks Bill for her name. He wonders why she's been attending his lectures as he knows she is not a student at the university. She admits that she actually works at the university canteen, but attempts to deny sneaking into the Doctor's lectures. He counters that he has seen her and asks again why she keeps turning up. After fumbling over a story about a girl she fancied in the canteen, Bill confesses that she loves his lectures and always wanted to attend the university. She then challenges him, asking why the man has taken an interest in her as "plenty of people come to [his] lectures that aren't supposed to". He explains that he has noticed her because she smiles when she doesn't understand something, whilst the majority frown.

Bill asks around about the Doctor, saying that it's rumoured he's lectured for over 70 years. The Doctor thinks she's asking about his age, but Bill says that she wants to know what subject he's supposed to be lecturing on. It seems he has permission to talk about whatever he wishes; on one occasion, he was supposed to give a lecture on quantum physics, but talked about poetry. He tells her that they're basically the same thing because of all the rhymes. The Doctor offers to be Bill's personal tutor, and sort out her enrolment with the university, on the condition that she comes to his office at 6pm every weekday (even if someone is dying) and that if she gets anything less than a First on every assignment, the tutoring will cease. As she leaves, she asks what she should call him, as everyone calls him the Doctor. He tells her it's what he's called. Bill is sure this cannot be his real name, asking "Doctor what?" The Doctor just smiles.

Bill goes through her daily routine: serving chips, attending the Doctor's lectures and tutoring sessions, and returning home to her foster mother, Moira. Bill explains that the Doctor is kind of her foster tutor, as Moira goes over Bill's assignments, where she has scored at least 87% in each subject the Doctor has taught her, even very obscure topics. Moira is worried that the Doctor might be some kind of paedophile, warning Bill to be careful of men. Annoyed, Bill mutters under her breath she's not interested in men.

The Doctor gives a lecture on the concept of the passage of time; in truth, time doesn't pass, because life is a great magician that only allows people to live one day at a time. As people remember living yesterday, they hope they'll live another day tomorrow. He further explains that each day is like a photo, a frozen moment, which, like a movie, when played in quick succession, comes alive. The Doctor tells his audience to imagine all time happening at once. Every moment from birth to death, all the triumph and heartbreak of their lives comprising an entire city; it's the best place a person can ever hope to be. Writing on the chalk board, the Doctor calls this Time and Relative Dimension in Space, going on to say "it's called life". That night, when out at the student bar with her friends, Bill's eye's meet those of another girl across the room. As she heads to the bar, Bill bumps into her and notices that the girl has a gold pattern like a star in her eye.

The next morning, Bill sees the Doctor and Nardole suspiciously hurrying through the university quad and decides to follow them out of curiosity. The pair descend into a hidden vault under the university, and Bill is surprised to find that the security door opens for her. She overhears snatches of their conversation but accidentally kicks over some clutter on the floor and fearing detection, hurriedly makes her way out again. Outside, she notices Heather, whom she recognises as the girl from the bar, sitting on a bench looking distraught. Bill asks if she is okay and enquires about the star in her eye, but Heather brushes this off as a "defect in the iris." Sensing that Heather is troubled, Bill asks if she is "freaking out about something." Heather hesitates, before asking Bill to come with her and see something; Bill accepts and they set off across campus. On the way Heather says that she hates the university but doesn't know why, remarking "Everywhere I go, I just want to leave." The pair arrive at a concrete service yard behind one of the university buildings, entering through a gap in the security fence. Heather points out a mysterious puddle on the concrete that ought not to be there, as it hasn't rained in a week. When Bill finds this unremarkable, Heather asks her to look at her reflection in the puddle and tell her what's wrong with it. Bill notices that her face does appear wrong in the puddle's reflection, but can't figure out how. Whilst Bill ponders the unsettling reflection, Heather is overcome by her desire to leave and walks off, though not without regret. Bill is left crestfallen, and leaves too. When the yard is empty again, a voice issuing from the dark liquid announces that the "pilot is located".

At Christmas time, Bill celebrates with the Doctor, giving him a rug as a present; though the Doctor admits that he hasn't gotten her anything. They discuss travelling, Bill saying that she can sense that the Doctor travels around, even though he denies it. She says "With some people you can smell the wind in their clothes." This is what she presumes her birth mother would have said, revealing that she died when Bill was young. Bill tells the Doctor that she apparently looks like her mother but doesn't know this as there are no photographs of her. She wonders whether photos really help after loved ones are gone, causing the Doctor to look wistfully at the photographs of his wife River and granddaughter Susan on his desk. At home, Bill's foster mother Moira shows her a newly discovered box containing photos of Bill's birth mother. Bill weeps upon discovering that she looks just like her mother. She notices the reflection in a mirror in one of the photos, in which the Doctor can be seen holding the camera.



Months later, Bill walks past the service yard again and is delighted to find Heather, who is once more staring into the puddle. Bill calls out and Heather smiles, though her demeanour is noticably different to the last time they met; there is a knowing look in her eyes. She asks if Bill ever worked out what was wrong with her reflection in the puddle. When Bill answers that she did not, Heather invites Bill to come round and offers to show her. Remembering her hasty departure when they last met, Bill asks Heather to promise not to go without her. Heather promises, but when Bill has run around the building and through the gap in the fence, her friend is nowhere to be seen. Assuming Heather to have walked out on her again, Bill is slightly offended, and leaves; not seeing Heather's screaming face beneath the surface of the puddle. As she is pulled down into the liquid, a voice announces "Pilot confirmed. Pilot engaged."

Worried about Heather and her fascination with the strange puddle, Bill consults the Doctor. She tells him about Heather's eye and the inexplicable reflection in the puddle. On hearing this, the Doctor runs out of his office to investigate, and Bill follows. The Doctor eventually figures out that the reflection looks wrong because it is not a reflection at all. He explains that when looking at your reflection you never see your face the right way round; it looks wrong in the puddle because it looks right. It was easy for Heather to spot because the star in her eye makes her face asymmetrical. Bill questions how it behaves like a reflection, leading the Doctor to conclude "It's not reflecting you, it's mimicking you. There's something in the water pretending to be you." He scoops up a sample in a test tube and examines the pattern of scorch marks on the concrete nearby. Sensing danger, the Doctor sends Bill home to keep her safe. As she heads off, the voice from the puddle declares "Passenger selected. Pursuit engaged" and the puddle begins to move. Back at her flat, Bill notices the sounds of someone in the bath, even though Moira is out that night. Bill runs to the university upon seeing Heather's starry eye staring out of her bathroom drain.

Outside St Luke's University, Bill is confronted by her pursuer. When Bill trys to speak to her however, she only mimics Bill's words. As Bill steps closer, she sees that liquid is constantly pouring over Heather's body, dripping off her hair and hands; her face is pale and expressionless. Bill is horrified, exclaiming "You're dead?" The creature suddenly glides towards her, but Bill escapes and rushes into the Doctor's office, where he is examining a sample of the liquid from the puddle. Though Bill bars the door, the puddle gushes under it and reforms into Heather. The Doctor convinces Bill to enter his blue box, taking the sign off as they do. Bill protests that the box can't save them only to turn around as the console lights up and the Doctor reveals the TARDIS. Coming to terms with its size, Bill claims she needs the toilet, meeting Nardole on her way down. The Doctor proceeds to take them down to the vault, where she realises that the police box in the corner of the Doctor's office is his spaceship, which is bigger on the inside. The Doctor and Bill infer that the puddle creature is not here for whatever is hidden inside the vault and is instead there to chase them. Even as they reach this conclusion however, liquid trickles down the steps and Heather reappears. She issues a piercing scream as the Doctor, Bill and Nardole escape in the TARDIS, which the Doctor flies to Australia to test the Heather creature's abilities.

In Australia, Bill asks the Doctor if he's from space; he tells her that he's not: "Nobody's from space. I'm from a planet like everybody else." Bill contends that the acronym TARDIS doesn't make sense then, as it only works in English, to which the Doctor replies that most people don't bring this up. Heather soon catches them up, forming out of droplets on a mirror, so the trio again escape in the TARDIS, this time to a planet on the other side of the universe, 23 million years in the future. Here, the Doctor hypothesises that the puddle is a type of sentient oil or perhaps a small part of a shape-shifting "liquid spaceship" which had lain dormant until it saw something it needed. On the Doctor's prompting Bill remembers Heather's desire to leave, explaining why the puddle chose her; it needed a pilot, someone who wanted to fly away. When Nardole asks why the creature wants Bill, the Doctor begins to suspect that it may be the result of the mutual crush she and Heather had on one another, asking: "What, in the end, are any of us looking for? We're looking for someone who's looking for us." As the Doctor says this, Bill looks into a pool of liquid she has found. Heather begins to rise to the surface, smiling at Bill, who smiles back. But then her smile fades and Heather grabs Bill, trying to pull her down. The Doctor and Nardole free Bill and they retreat to the TARDIS, as liquid gushes out of the pool and begins to reform.

The Doctor's last test of Heather's abilities is to run her through "the deadliest fire in the universe". Nardole is terrified of where they're going; the Doctor hands him the Fourth Doctor's sonic and tells him to run interference. Once they land, Nardole runs off in the opposite direction. The Doctor leads Bill to a skirmish in the Dalek-Movellan War. They are found by Heather, who is shot by a Dalek; but the blast goes straight through her and she reforms after it. The Dalek fires in vain as the Doctor and Bill run. They are then confronted by a Dalek, but when it appears to malfunction, the Doctor realises something is wrong with it. He looks into the Dalek's eye stalk, which is displaying the striking star pattern of Heather's eye. The Dalek dissolves and reforms as Heather. The Doctor infers that the creature doesn't mean to harm Bill, as it didn't use the Dalek's weaponry. He challenges Heather, demanding she leave Bill and fly away; asking "why won't you just go?" At this, Bill suddenly remembers that the last thing Heather said was a promise not to leave without her. "Never underestimate a crush" the Doctor notes, as they realise that Heather is inviting Bill to fly with her. The Doctor tells Bill to release Heather, so Bill sadly absolves her of the promise, telling her "I really liked you." However, Heather reaches out her hand to Bill, who takes it, in spite of the Doctor's protests. As their hands clasp a sphere of water surrounds them and Bill sees a stunning vision of planets and stars interspersed with Heather's memories of their mutual attraction. The Doctor tells Bill to resist, still fearing the possiblity that it is a trick. Bill sadly says goodbye to Heather, to which Heather responds "Goodbye, Bill": the first thing she has said since her transformation that is not mimicry, indicating that Heather remains herself and is not possessed. Heather departs leaving Bill shaken and upset.

The Doctor brusquely returns to his ship while Nardole comments on the former's seemingly ignorant behaviour. Bill comments that the tears she sheds don't feel like her own.

Back in the university office, Bill seems to regret her decision not to leave with Heather, asking the Doctor if they will see her again and looking hopefully at the TARDIS. The Doctor says that she must forget about seeing Heather or travelling in the TARDIS and tries to wipe her memories of doing so, explaining that he must remain in disguise, unknown to everyone owing to a promise he made. Bill retorts, asking how he would feel if someone tried to wipe his memories. The Doctor tells Bill to leave immediately without another question, before he changes his mind. He looks at the picture of River, telling it to shut up, then the same for Susan's picture. Even the TARDIS briefly hums causing the Doctor to confess he "can't keep doing this".



Outside, Bill runs down the steps, checks that she can remember Heather, and smiles. She finds the Doctor leaning on his TARDIS on the university courtyard. He tells her that it's a big universe, but maybe one day they will find Heather. When Bill asks what caused him to change his mind, the Doctor responds "Time and Relative Dimension in Space. It means what the hell." Bill excitedly runs into the TARDIS, followed by the Doctor, who shuts the door behind them. Now the Time Lord is ready to see the universe anew.

Cast

 * The Doctor - Peter Capaldi
 * Bill - Pearl Mackie
 * Nardole - Matt Lucas
 * Moira - Jennifer Hennessy
 * Heather - Stephanie Hyam
 * Voice of the Daleks - Nicholas Briggs

Science

 * The Doctor is Bill's tutor on physics and astrophysics, among other subjects.
 * The Doctor says quantum physics and poetry are the same thing.
 * Bill's graded paper on The Cosmic Far Ultraviolet Background mentions blazars which are members of the galactic nuclei and quasars, polarization, the Pittsburg Conference on BL Lac Objects.
 * Bill's graded paper on quantum statistics of light mentions the atom, electrons, protons, trees, balls, automobiles.
 * Bill's graded paper on Laser cooling of ions: atomic clocks and quantum jumps mentions ions and a few words from the Lord.
 * The Doctor lectures on Time And Relative Dimension In Space, saying it means life and so references past days and future days, present days, little moments, big moments and hypotheses them all happening at once.

Technology

 * The Doctor has, in his office, several sonic screwdrivers, of various designs from his past.

TARDIS

 * The Doctor tells Bill that "TARDIS" stands for "Time and Relative Dimension in Space" (Some other stories have it as "Dimensions"). Bill points out that this acronym would only ever work in English.
 * Bill compares the TARDIS control room design to a kitchen.
 * She also asks where the toilet is.
 * While she discovers the TARDIS is bigger on the inside, Bill at first thinks it's a knock-through behind his office, then that it's a lift.
 * The TARDIS has a macaroon dispenser.

Culture

 * Bill is a fan of science fiction, and recognises many of its tropes in her experiences with the Doctor, including mind wipes.
 * Bill watched a thing on Netflix about lizards in people's brains, controlling them.
 * Moira has a Crock-Pot Cookery cookbook in the kitchen.

Food and beverages

 * Bill serves chips.
 * The Doctor drinks water during his lectures.
 * The Doctor mentions vegan wraps.
 * The Doctor jokes that the air and sky on the alien planet is made of lemon drops.
 * The Doctor rhetorically ask Bill if she thinks her bacon sandwich loves her back.

Species

 * The Dalek doesn't recognise the Twelfth Doctor until it scans the sonic screwdriver, as according to its own knowledge at the time, the Doctor has brown curly hair and is wearing a long scarf.

Locations

 * While running away from the sentient oil puddle, the Doctor, Nardole and Bill visit various locations.
 * They visit Sydney in Australia, specifically Kirribilli, with a view of the Opera House.
 * They visit a planet on the other end of the universe.
 * They visit a war zone in the Dalek-Movellan War.

St Luke's University

 * The Doctor has been lecturing at St Luke's University in Bristol for apparently 50 years.
 * Bill serves chips there, and Heather is a student.
 * The Doctor's office contains the TARDIS, photographs of River Song and Susan Foreman, Rembrandt van Rijn's Self Portrait with Two Circles, black-and-white prints of Joshua Reynolds' Portrait of Emma Hart and George Romney's Lady Hamilton in a Straw Hat, and busts of Ludwig van Beethoven and William Shakespeare. He also has an old-fashioned radio, a record of His Master's Voice and a gramophone.
 * Bill comments that both the doors and windows in the office are too small to have brought the police box in without taking it apart.
 * The Doctor and Nardole are keeping something hidden in an underground vault beneath the university.

People

 * Nabeela is a member of staff at St Luke's University.
 * Mrs Potts died when Bill was a baby.
 * Neville is Moira's ex-boyfriend.
 * Barry is Moira's friend.

Music

 * A choir is singing "Jingle Bells" during Christmas.

Story notes

 * A working title for this episode was A Star In Her Eye.
 * Before filming started, a two-minute promo teaser introducing Bill known as Friend From the Future was broadcast in April 2016. Parts of this promo were adapted into the episode during the encounter in the Dalek war zone. (DWM 511)
 * The read-through for The Pilot took place on 14 June 2016, and filming on the episode began on 20 June.
 * The song "Love Will Tear Us Apart" by Joy Division plays during the bar scene, when Bill and Heather first meet.
 * Bill mentioning people being possessed by lizards in the brains is a reference to the Stargate franchise.
 * When the Doctor finally invites Bill onboard the TARDIS, he says "Time And Relative Dimension In Space, it means... what the hell." it is a reference to the scene in Back to the Future in which Doc Brown tells Marty he broke the space-time continuum by avoiding death.
 * During the scene in which the TARDIS travels to the Dalek-Movellan War Zone, a short scene from TV: The Doctor's Wife is re-used in which the TARDIS leaves through the bubble universe rift for the House planetoid.
 * As described by Caroline Lie, many if not all of the extras who attend the Doctor's lecture were employees from Doctor Who Experience in Cardiff. She can be seen, in fact, in multiple places, often near her friends, including Joe (TARDISArchives). Both previously participated in Classmates, a YouTube series consisting of fan reactions to episodes of Class.
 * The setting of this story bears some resemblance to the unfinished TV story Shada. Both stories feature Time Lords (in Shada, Chronotis; in The Pilot, the Doctor) who settle in colleges as eccentric professors for an extended period of time. Both feature opening shots of a student (in Shada, Chris Parsons; in The Pilot, Bill Potts) entering their studies and noticing the TARDIS, parked in the corner.
 * During the scene when the Doctor is about to wipe Bill's memory and she tells him to imagine if someone did it to him, "Clara's Theme" plays. This is a reference to the events of TV: Hell Bent.
 * "The Sad Man with A Box" plays in the scene in which Bill is introduced to the TARDIS. A happier, more fairy-tale rendition of this same tune, "The Mad Man with a Box", played during the scene in The Eleventh Hour when Amy walked into the TARDIS and saw the interior for the first time.
 * The Doctor uses a chalkboard with the same white roundel frame in his university classroom as Miss Quill does in her classroom at Coal Hill Academy in the spin-off Class.
 * The romance between Bill Potts and her friend, Heather, may be homage to William "Bill" Hartnell, the first actor to portray the Doctor, and his wife, Heather Hartnell.
 * The ringtone for Bill's mobile phone is the same as the one for Martha Jones' phone, which was later kept onboard the TARDIS by the Tenth Doctor.
 * When Nardole shows Bill the Doctor's office, his arm makes a mechanical sound and a bolt falls from it, implying that his body is robotic, or at least partially cybernetic.
 * Pearl Mackie is added to the title sequence in place of Jenna Coleman and is immediately followed by "and Matt Lucas", bridging the gap between actor names in the previous episode. The Doctor's face also appears after the show's title now.
 * According to Doctor Who Magazine #512, two scenes were filmed, but edited out before broadcast. One features Bill asking Nardole about the Doctor; the other was an alternate edit of the club sequence where Bill meets Heather for the first time. As originally filmed, Bill was to be shown watching the Doctor, on stage, sadly playing Clara's Theme. The only remnant of this in the final episode is a brief glimpse of the neck of the Doctor's guitar and his left hand.
 * This episode includes both a "Next Time" trailer for the following episode and a "Coming Soon" trailer for the remainder of the season. Making this the first episode that contains both a next time trailer and a coming soon trailer.

Myths and rumours

 * The episode was to include a "very mild" sex scene between Bill and another character. This rumour circulated widely on Twitter in the months prior to broadcast, allegedly citing an advance copy of the episode and emerged in conjunction with the (later confirmed) rumour that Bill would be gay. There is no indication such a scene was ever actually scripted or filmed.
 * The character of Bill and Heather, who become attracted to each other, are named for William Hartnell and his wife, Heather. Steven Moffat has confirmed that this was a coincidence.

Ratings
The overnight ratings on BBC One were 4.64 million, up 60,000 viewers from the previous series opener, The Magician's Apprentice. Consolidated figures were 6.68 million, the highest figures for a standard series episode since the Series 8 finale, Death in Heaven.

Filming locations

 * The Main Building, the Sir Martin Evans Building, and Tower Building of Cardiff University largely fill in for St Luke's University, while the Reardon Smith Theatre (within the National Museum of Wales) is where the Doctor gives his lectures.
 * The Cardiff Metropolitan University (Llandaff Campus)'s Atrium Cafe is where Bill serves chips.
 * The bar scene was shot at Clwb Ifor Bach in Cardiff.
 * Bill runs into the bathroom in "Australia", in World of Boats in Cardiff.
 * CEMEX's Taffs Well quarry, just outside of Cardiff, is the exotic planet the TARDIS team travel to.

Production errors

 * Bill is wearing a completely different shirt when she gets back to the university after Heather leaves.

Continuity

 * Nardole's arm makes a mechanical noise and drops a bolt, hinting at his previous removal from King Hydroflax. (TV: The Husbands of River Song, The Return of Doctor Mysterio)
 * The Doctor has a mug filled with his former sonic screwdrivers in his office, as well as hidden in the TARDIS. (TV: Fury from the Deep, The Dominators, The War Games - The Visitation, Doctor Who, Rose - The Witch's Familiar)
 * The Doctor has framed photographs on his desk of both his lost wife River Song (TV: The Wedding of River Song, The Husbands of River Song, et al.) and his granddaughter Susan. (TV: An Unearthly Child-The Dalek Invasion of Earth et al.)
 * The Doctor has a jeweller's eyeglass. (TV: Heaven Sent)
 * The Doctor has an "Out of Order" sign on the doors of the TARDIS, nearly identical to one used by his first incarnation. (TV: The War Machines)
 * The Doctor and Bill are wearing paper hats and pull Christmas crackers. (TV: The Christmas Invasion, The Time of the Doctor, Last Christmas)
 * The Doctor has a wooden raven on his desk in his office. (TV: Face the Raven)
 * The Doctor still has blackboards in the TARDIS. (TV: Into the Dalek, et al.)
 * Bill says the TARDIS is bigger on the inside than it is on the outside. (TV: The Three Doctors, et al.)
 * Nardole explains the concept of the TARDIS dimensions. (TV: The Robots of Death, In the Forest of the Night)
 * The Doctor and Bill are bantering. He was previously against that. (TV: Robot of Sherwood, The Woman Who Lived)
 * The Doctor's Rembrandt van Rijn portrait Self Portrait with Two Circles appears in his office. (TV: The Husbands of River Song)
 * The TARDIS goes to Australia. (COMIC: Gemini Plan, Backtime, TV: The Enemy of the World, A Christmas Carol)
 * The reveal of the TARDIS strongly resembles how the Ninth Doctor revealed it to Rose Tyler, with Bill mirroring Rose's resistance to initially enter, sceptical it is safe. (TV: Rose)
 * The Doctor has previously met sentient liquid beings: the Kar-Charratans on Kar-Charrat (AUDIO: The Genocide Machine) and the Flood on Mars. (TV: The Waters of Mars)
 * The Doctor previously encountered a creature which mimicked living people to steal their form. (TV: Midnight)
 * The Doctor encountered before another spaceship part seeking a compatible pilot, who wanted to leave and travel. (TV: The Lodger)
 * The Doctor mentions all of time hypothetically happening at once, during one of his lectures on time. He once experienced such an event. (TV: The Wedding of River Song)
 * The Doctor and his companions have before been chased throughout time and space.
 * The First Doctor, Ian Chesterton and Barbara Wright were once chased by the Daleks. (TV: The Chase)
 * The Tenth Doctor and Martha Jones were chased by the Family of Blood. (TV: Human Nature, The Family of Blood)
 * The Eleventh Doctor and his team were once chased by The Then and the Now. (PROSE: Doctor Who: The Eleventh Doctor Year 2)
 * The Twelfth Doctor once said that a Quantum Shade could chase a person throughout all time and space if marked. (TV: Face the Raven)
 * The Doctor plays his electric guitar. (TV: The Magician's Apprentice, et al.)
 * The Doctor is wearing his sonic sunglasses. (TV: The Magician's Apprentice et al.)
 * The Doctor repeats the anagram of TARDIS as "Time and Dimension in Space", while also saying it means life. (TV: Rose)
 * In his office, the Doctor has his bust of Beethoven, previously seen in his TARDIS. Similarly, he also plays Beethoven's Fifth Symphony. (TV: Before the Flood)
 * In his office, the Doctor also has a bust of William Shakespeare. (TV: The Chase, The Shakespeare Code)
 * As Heather follows Bill, the Doctor says you should never underestimate a crush, and Nardole says he didn't have to tell him. (TV: The Return of Doctor Mysterio)
 * The Doctor tells Bill that being scared is good and rational. He previously told Rupert Pink similar, (TV: Listen) and would later repeat this sentiment with Bill and Nardole. (TV: Oxygen)
 * The Doctor pulls out his psychic paper. (TV: The End of the World, et al.)
 * Bill writes an essay entitled "Laser cooling of ions: atomic clocks and quantum jumps." The Eighth Doctor encountered an atomic clock on the eve of the new 2000th year. (TV: Doctor Who)
 * The Doctor pilots the TARDIS to the Dalek-Movellan War. (TV: Destiny of the Daleks)
 * The Movellans reappear. (TV: Destiny of the Daleks)
 * Near the vault, the Doctor has a sign belonging to the Mary Celeste. (TV: The Chase, PROSE: The Mystery of the Marie Celeste, COMIC: A Stitch in Time)
 * The Doctor had encountered scorch marks left in concrete by a shuttlecraft once before, also on a school campus. (TV: Remembrance of the Daleks)
 * The Doctor mentions the TARDIS' broken chameleon circuit, (TV: An Unearthly Child, Logopolis, Boom Town, COMIC: Hunters of the Burning Stone, et al.) and calls it a "cloaking device". (TV: Doctor Who)
 * The Doctor attempts a memory wipe. (TV: Journey's End) He previously revealed that he's done this several times, usually telepathically. (TV: Hell Bent) In this case, the method he's about to use was the same one employed on Donna Noble. (TV: Journey's End)
 * The Doctor relents on wiping Bill's memory when she poses the question of how he would feel if it happened to him, clearly bringing back his memories of forgetting Clara Oswald. (TV: Hell Bent)
 * The Doctor clicks his fingers to open the TARDIS doors. (TV: Forest of the Dead, The Eleventh Hour, Hell Bent, et al.)

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Digital releases
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