Smile ( TV story ) It also reused the theme of killing unhappy people , which had previously been seen in the Seventh Doctor story , " The Happiness Patrol " " , " where the tyrannical Helen A outlawed anything remotely sad , and executed anyone who disobeyed . The Vardy are shown as a swarm of intelligent beings , capable of reducing people to nothing but bones in mere moments . This makes them a mechanical counterpart to the Vashta Nerada , but only in this ability . This marks the fourth time in the Revived Series that the Doctor has taken his companion into the future for their second adventure with him after Rose Tyler , Amy Pond and Clara Oswald . It appears the Doctor has also come to accept that he doesn ' t always get to go where he wants ; by this point , he has decided to negotiate with his TARDIS as to where it will take him . In " Doctor Who Extra " , Steven Moffat and Peter Capaldi explain that they don ' t really understand Emoji . Thus they have some trouble understanding texts from Jenna Coleman , who uses Emoji frequently in her texts . Synopsis . After shaking off Nardole , The Doctor asks where Bill Potts wishes to travel in time . She asks to see the future . Complying , he takes her to see one of Earth ' s first space colonies , where it ' s been stated the inhabitants have cracked the secret of perpetual happiness . However , they soon discover that the cause of this " happiness " has a very deadly punishment for not following along . Plot . Bill has just entered the TARDIS , asking the Doctor what she should do as a passenger . The Doctor tells her that she should know as she ' s already been on a trip . Bill counters this by stating it ' s a proper trip this time , asking if there are seat - belts . She sits in a seat , noting that the layout the TARDIS is completely wrong ; the seats are too far away from the controls . She wonders if the Doctor can stretch his arms like Mr . Fantastic of the " Fantastic Four " . The Doctor explains he stands when piloting the TARDIS . Bill mocks him for never thinking to bring the chairs next to the controls . Bill then asks where the steering wheel is . The Doctor tells her that they have to negotiate with the TARDIS ( as it ' s sentient ) , as it will not always take them where they wish ; often it ' s the " still point " between where one wishes to go , and where they are needed . ( In other words , sometimes the TARDIS does take the Doctor where he wants , but WHEN is up to it . ) Hearing a knock , Bill wonders who could be knocking on the TARDIS doors . The Doctor mumbles " mum " and opens the door . Nardole enters , reminding the Doctor that he made an oath and cannot leave the Earth unless a emergency happens . The Doctor tells Nardole that he ' s over 2000 years old and sometimes likes to take his TARDIS downstairs instead of walking . Nardole asks why Bill is inside ; the Doctor states it ' s because she isn ' t anywhere else . The Doctor kindly asks Nardole to make tea . Nadrole agrees and leaves them ; he states if Bill wants tea , she have to make her own . Thinking that the Doctor has changed his mind again , Bill asks if they are heading back to his office , to which the Doctor states will happen , after they ' ve had some adventures ; " between here and my office is everything that ever happened or ever will . " The Doctor tells Bill to make her choice : past or future . Bill states the future , because she wants to see if it ' s happy . The Doctor complies , throwing the brake lever and the TARDIS takes off . In a future human colony planet , a colonist , named Kezzia , is warned not to come back to the city as they are having a problem with their microbots , the Vardy ; however , she ignores the warning , as she talks to a robot with an emoji - like screen . The woman on the radio , named Goodthing , is smiling painfully as Kezzia asks why she ' s doing it . Smiling still , she explains that their mother and a few other people are dead . Kezzia is horrified to see her smiling at that , prompting another robot to display a crying emoji . The robot ' s screen turns to a emoji with skulls for eyes and bared teeth ; it grabs Kezzia as a section of the roof transforms into a swarm of microbots . It envelops Kezzia and reduces her to bones as they scream . The robot turns to Goodthing , still displaying the emoji , as she pleads with it that she smiling , the microbots chase after her as she screams , while the screen turns back to a happy emoji . The TARDIS materialises there later , with Bill asking which direction Earth is in . The Doctor tells her any direction , as space is curved ; he asks if she ' s wanting to go back . Bill states she isn ' t thinking of anything ; her mind is " overloading " from time travelling to an alien planet in the future . As they walk towards the city , Bill notes the TARDIS hasn ' t cloaked itself as something else . The Doctor reminds her that it ' s stuck ; Bill notes that the Doctor must like it enough to have never bother to fix the broken cloaking device . Annoyed , he tells her to let the subject go . They walk into the city , where the Doctor explains that this place was able to crack the mystery of perpetual happiness . Bill then questions the Doctor about what Nardole said . The Doctor explains that as a result of something that happened a long time ago , he swore an oath to watch the vault beneath the university . Bill points out that he isn ' t right now . However , the Doctor counters that he IS guarding it , as his time machine can take him back to right when he left . Bill questions the Doctor as to whether or not he ' s considered the possibility of him getting stuck or lost away from the university . The Doctor tells Bill that he ' s thought of it , and has decided to not dwell on things that haven ' t happened yet . Bill catches sight of the Vardy , asking if they ' re alien birds . The Doctor tells her they are microbots , and that they are likely conducting a security check on the two of them . Bill is disappointed with the robots ; the Doctor tells her not to say such things , as it ' s rude . Bill sarcastically asks if she hurt their feelings . Feeling pain in their ears , Bill wonders what happened . The Doctor shouts they ' ve been fitted with some kind of communication device ; bizarrely his voice comes out her ear . Bill notes how wonderful this is ; she ' ll never need her mobile phone again . However , she then becomes concerned about being able to turn off the device when using the loo . The Doctor dismisses her worry , stating if they can be given a communication device without any fuss , " there ' s probably an app for that . " They come across a robot , which Bill is impressed by . However , the Doctor tells her it ' s not a robot , but instead a interface device to interpret for the Vardy . Bill wonders if it speaks ; the Doctor says it depends on what factor of human language has survived into this era . The robot ' s face smiles , with two smiling faces for eyes . Bill laughs that it speaks emoji ; the Doctor is less than impressed . The Emojibot gives them badges that reflect their mood s in the form of emojis , which only other people ( and not the user ) can see . Placing the badges on , both the Doctor and Bill are surprised that they instantly go to their backs . The Doctor presumes that this is so that seeing one ' s own emotion on the badge doesn ' t change it , which would have caused a " feedback loop " . Bill questions this , as what if the wearer fancies someone ; the Doctor laughs , " Well , I guess you ' d have to maintain eye contact with them , then . " Bill thinks the idea is brilliant . . They head further inside , while Bill ' s badge shows her happy , the Doctor ' s shows him as puzzled . Since the interface speaks in emoji , the Doctor postulates that the entire city was developed by teenagers ( since they use emoji in texts . ) The Emojibot serves cubes of gelatinous blue food ; Bill notes the cubes smell like fish . The Doctor says he is not fond of fish , except for conventionalising ; thus eating less evolved fish would lead to an awkward conversation . Bill wonders if the food is safe for them to eat , as she doesn ' t know if humans are meant to be living here ; the Doctor points out that the cutlery is human and only humans speak in emoji . Bill begins eating her cube of food . Seemingly responding to the Doctor ' s puzzlement , a swarm of Vardy wait outside the building . The Doctor notices there is no livestock , to which Bill is pleased to know that humanity no longer needs to eat animals ; instead , this algae - like substance . The Doctor notes he meet an emperor made of algae once , piquing Bill ' s curiosity ; the Doctor adds the emperor fancied him . The Doctor reiterates that this place is ready for humans to live in , as the entire place is ready for someone to move right in , but there is no - one around . Bill compares it the student union , where a place to live is prepared before anyone moves in . Seeing Bill is on to something , the Doctor comes to the conclusion they ' ve just arrived too early ; the colonists sent the Vardy ahead of them to prepare the planet for them . The Doctor goes on to note that if the atmosphere wasn ' t human - friendly , the Vardy would fix it for them ; even better , the robots could build a home for the colonists to live in before they got there . However , Bill notes that the Doctor has two helpings , wondering if there ' s food sexism in the future ; " is this bloke utopia ? " The Doctor explains that it ' s likely because the Vardy have mistaken him for two different people ; as the Vardy work for humans , they do not understand the concept of a person having two hearts and thus think the Doctor is two people . Bill is surprised , wondering why the Doctor has two hearts ; he retorts " why one ? " Finishing her meal , an amused Bill wonders if the Doctor has really high blood pressure as a result of having two hearts . He confirms this . The Emojibot escorts the Doctor and Bill to a greenhouse outside , where more Emojibots pollinate plants and an automated system sprays calcium - based fertiliser onto the plants . The Doctor finds a discarded necklace , keeping it hidden from Bill . Bill wonders what they should do : leave before the colonists show up , or put the kettle on . The Doctor walks past her into the next room , where Bill notices a rosemary plant . Bill smells it , remembering there ' s one outside the student union . She thanks the Doctor for bringing her ; she ' s smelling the scents of home several years into the future . The Doctor asks if Bill believed his theory about there haven ' t been any humans here yet ; Bill confirms she did . He then asks if he convinced himself ; Bill looks at his badge and tells the Doctor that he didn ' t . The Doctor then goes on the explain that he is worried because there should be a set - up team of humans commanding the Vardy . However , no - one is here . Noticing the Doctor ' s badge has a thinking face , Bill asks what ' s on his mind , and he replies , suspicious that he is thinking about " a magic haddock " . As they have no answers , the Doctor decides they should put two questions together : where is the set - up team and what is the source of this mineral fertiliser ? Pulling out his sonic screwdriver , the Doctor opens the machine pumping the fertiliser ; it has grinding gears pulverising calcium . He then opens the bottom , revealing several skulls . The Doctor tells Bill that despite how this appears , the humans haven ' t been dead long . He has come to the conclusion that the Vardy killed the set - up team and feed them into the fertiliser . Bill wonders why , to which the Doctor says they ' d better not stick around to ask them . They turn to find an Emojibot with a crying face . The Doctor tells it that they were admiring the garden and are leaving now . They run out the room , as the teary - eyed Emojibot changes to show the same emoji that it showed when the women were killed . As they run , Bill notes that if the Emojibot is chasing them , it ' s being awfully slow . The Doctor explains to Bill that there ' s a reason for something chasing you to be slow , when it ' s targets are running ; the chaser doesn ' t need to be fast . In the centre of a corridor , the Doctor and Bill find themselves surrounded by Emojibots that can sense their fear . The city is full of them , so the robots will catch you eventually ; thus making a chase pointless , as they can maneuvre targets into a trap . The Doctor wonders why they ' re being attacked NOW , when they ' ve been there a long time . Realising something , the Doctor tells Bill to smile using her whole face ; she wonders why as the Doctor checks her badge . Seeing Bill ' s badge change to a smile , the Doctor tells her that smiling has a psychological effect on one ' s mood . He further explains the robots ' programming has caused them to make these mistakes ; the Vardy were programmed to make people happy by ensuring their environment was comfortable , but the programming has evolved and gotten jumbled up somehow . The Vardy now seem to think that they need to kill people when they become unhappy . The Doctor tells Bill they should give the Emojibots what they want , and smile . The Doctor starts walking down the exit hall , telling Bill to not even bother following him unless she is smiling . They slowly walk down the hall . The Doctor tells the robots that they ' ve enjoyed their stay . Bill tells him that next time , they should go to Aberdeen or Wiltshire . Agreeing with her , the Doctor and Bill move past the Emojibots , now bearing annoyed faces , but still poised to attack . They run outside , where an Emojibot grabs Bill ' s arm . Bill screams in terror , as the Doctor tells her to smile . However , Bill is too scared to fake happiness . Instead , the Doctor sonics the robot ' s arm , breaking it and freeing Bill . This signals a swarm of Vardies to seemingly emerge from the building ' s structure itself . They continue running , with the Doctor sure the Vardy will not be concerned with them once they are out of the city . Once back at the TARDIS , the Doctor tells Bill to stay in inside while he returns to the city and follows a " childish impulse to blow it up . " Bill is flabbergasted , as she thought they were leaving . Surprised Bill cannot see the bigger picture , the Doctor explains " that city is a living death trap ; we can ' t leave it with it ' s mouth open . " As there is likely a colony ship coming , they have to ensure that the Vardy do not claim anymore lives due to the error in their programming . The Doctor tells Bill to watch some movies in the TARDIS . Bill wonders why he can ' t call a " helpline " to deal with the problem instead , the Doctor runs off , telling her not to look at his browser history . Seeing the Doctor run , Bill heads back outside the TARDIS , reading the sign on the door : " Advice and assistance obtainable immediately " In the city , the Doctor convinces an Emojibot that he is happy , but his happy - faced badge changes to show a light bulb shortly afterwards . He hears someone breathing on his communication device ; thinking it ' s a survivor , he asks the person to join him . To his annoyance , it ' s Bill , who asks if he ' s Scottish because of his accent ; the Doctor says he isn ' t , just cross . Bill then wonders if there ' s a " space Scotland " too . The Doctor notes Scotland demands independence from every planet they land on . Bill tells the Doctor her deduction ; he doesn ' t call a helpline because he ' s it . He gives advice and assistance . The Doctor tells her that is just a coincidence ; he just happened by this house of horrors , and decided to muck in . He tells Bill to look at the wall , going on to explain that the Vardy are what makes up the city . Bill genuinely smiles at the absurdity . However , the Doctor believes that the centre of the city houses the spaceship in which the colonists first arrived , comparing it to the Vikings , who lived in their ships until they built new homes . They follow a staircase downwards , finding a damaged ships ' s hull ; the Doctor is glad to have found a real wall . Finding the entrance to ship , Bill tries to pull the door open to no avail . Humorously , the Doctor presses a button that opens the door inward . " Not even locked ; they were expecting to live in peace " the Doctor sadly notes . He then suggests locking it behind them , which alerts all Emojibots in the city , whose smiley emojis now incorporate exclamation marks for eyes . Inside the spaceship , the Doctor comments on the difference between design of the ship interior and the city outside , each designed by " wet brains " ( humans ) and " dry brains " ( Vardies ) . They come across a map labelling where they are , and the Doctor plans to walk to the engine room in the middle of the ship . He instructs Bill to stay back to guide him through the map , which displays the Doctor ' s current position . On his way , the Doctor finds all sorts of furniture and artifacts , including the bust of Nefertiti . Bill asks how the Doctor is allowed to blow up the spaceship without consequences , but he responds that it is a " moral imperative " to destroy the " murder machine " that surrounds them . Bill notices an unexpected empty space surrounding the engine room , but the tannoy of the ship distracts her . Outside , the Emojibots ' faces change to skulls as the ship , " Erehwon " , begins to wake up , and as the Doctor descends into the engine room . Bill realises she could have followed the Doctor the entire time if she had photographed the map . The Doctor reveals that he had already memorised the map , as Bill protests against his leaving her " out of trouble " . Bill follows the Doctor ' s path , but she stumbles upon a room containing a recently deceased old woman , with a book placed at her feet . Bill finds that the book contains digital images of human history on Earth , continuing past her time and through an apocalyptic war . Bill asks the Doctor these colonists were the last of humanity . The Doctor explains that humans evacuated Earth following this conflict , and that this colony must be one of those evacuative ships . He meanwhile fiddles with the engine room controls , trying to reroute the engine ' s flow into the calorimeter . However , as he tries to do so , the calorimeter begins to rise to its peak , which spells doom for the Doctor . Bill proceeds to the engine room , but to her shock , finds a boy , who asks , " Are we there yet ? " Meanwhile , an Emojibot closes in on the Doctor , who is still waiting for Bill to help him hold the calorimeter tightly while he jams it shut with a spanner . The Doctor sees its reflection in a dial , and smashes the emojibot off the catwalk with the spanner , nearly dragged down himself , only to run into Bill and the confused boy , who asks where everyone else is . The Doctor is puzzled by this , until he and Bill find that the empty space around the engine room is where the remaining human population is cryogenically stored . Shocked and disgusted with himself , the Doctor tells Bill that the colonists were already there , waiting to sheparded into the new utopia . One of the stored humans , named Steadfast , wakes up , and the Doctor assertively instructs him to stay inside the ship as the other humans begin to unfreeze behind him . The Doctor explains to Bill that he doesn ' t have a plan yet , but he acted like he had one to make sure idiots didn ' t cause more trouble by trying to think up their own plans . Bill takes the Doctor to the old woman ' s corpse , and they try to understand history and the woman ' s role in it . They discover a large number of deaths increasing in numbers since the death of this woman , the first death of the colony . The Doctor realises that it was grief that led to the deaths of all the people . The Vardies , not knowing how to interpret grief ( after a loved one has died ) , so they interpreted it as a threat to happiness that needed to be killed . Subsequently , all the grieving loved ones of every next person killed . In the short period of a day , sadness has become much like a plague . The Doctor again mentions the magic haddock , and produces the discarded necklace , which contains a hologram of the boy waving happily . Bill says that they will find the owner of the necklace when she wakes up , but the Doctor tells her that he found it in the greenhouse , belonging to one of the dead advance colonists . Meanwhile , an Emojibot offers a mood badge to the boy , who is walking outside in the city , looking for his mother . His mood changes to a puzzled emoji . Back to the Doctor and Bill . They ' ve finished explaining what ' s happened , and what ' s the first reaction of the human race ? The waking colonists arm themselves with laser guns to fight the Vardies . Bill tells Steadfast that he needs to listen to the rest of the explanation ; he bluntly says he did listen , now knowing that the Vardy are killing people . The Doctor quickly runs up to Steadfast , explaining " The Vardy want to help you ; killing you is just a side - effect . " . The colonists take off to destroy the Vardy ; the Doctor and Bill run after the colonists to prevent another mass slaughter . In the city , everyone finds the boy flanked by two Emojibots . The boy asks where his mother is , beginning to cry . Bill tries silencing him into smiling , telling him to admire his new home ; however , the boy doesn ' t listen and cries . The Emojibots grab the boy , ready to kill him ; however , Steadfast fires upon the Emojibots . One is damaged and the second ' s screen begins flashing between two new images . The Doctor realises that the symbols mean " Rage " and " Revenge " . The rest of the colonists begin to fire , as some Vardies break off from the ceiling to attack , and kill a man . Instead of caring about the attack , the Doctor begins thinking about how the Vardy are reacting ; they are registering as under attack . That means they ' re " alive " AKA sentient . He runs to a broken Emojibot , using the sonic screwdriver on its wiring . The Doctor tells Bill there ' s a reason he never loses at chess ; he has a secret move . Whenever he ' s about to lose , he kicks over the board and ends the game . Hoping what he ' s about to doesn ' t hurt , the Doctor finishes messing with the Emojibot , creating a blinding , disorienting flash throughout the city . The Doctor tells the story of the fisherman and the magic haddock . A fisherman caught the fish and it offered three wishes in exchange for it ' s life . The fisherman wished for his son to return from war and 100 gold pieces , but the haddock thinks in a different way ( like a robot ) , instead sending the son ' s corpse home from the war , along with 100 gold pieces commending his service . The fisherman then wished that he hadn ' t wished the first two wishes , pressing the " reset button " . The colonists are now confused as to why the Vardy aren ' t killing them . The Doctor repeats that he hit the rest button , basically turning the Vardy on and off again ; as a result they no longer remember murdering the humans or the fact they are robots belonging to the colonists . " Welcome to your new planet . Meet the Vardy . They are , as of now , the indigenous life - form . " The Doctor tells Steadfast that the colonists should try making peace unless they ' d rather live like homeless people as the waking colonists have no clue how to work the technology . Walking over to an interface , the Doctor introduces himself and apologises for not recognising the Vardy as an emergent new species . As penance , he is willing to negotiate with them to allow humanity to stay in the city ; he asks if the Vardy wish to charge rent . Returning to Earth in the TARDIS , Bill asks the Doctor if the human - Vardy relationship will work . The Doctor replies that it is up to them . Bill asks him if he normally deals with such affairs , acting as an " intergalactic policeman " . The Doctor replies that the police box exterior of the TARDIS is a mere coincidence . They land , exactly at the point they left , but when Bill steps out of the TARDIS , it is snowing . To their shock , elephant is approaching the TARDIS . The Doctor explains that they are in London , not Bristol , and that they are standing on the frozen Thames . Seeing this , the Doctor realises Bill might have been right about a steering wheel . Home video releases . DVD releases . " to be added " Blu - ray releases . " to be added " Digital releases . " to be added " External links . " to be added "