The Pilot ( TV story ) 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 Dalek s , 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 Movellan s 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 lecture s 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 , since the doors looked wooden and they had windows , 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 . Story notes . 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 " . Home video releases . DVD releases . " to be added " Blu - ray releases . " to be added " Digital releases . " to be added " External links . " to be added "