The Doctor Falls ( TV story ) Expanding on the Twelfth Doctor ' s regeneration teased in the previous episode , it saw him mortally wounded in battle against the Cybermen . The regeneration would also begin twice , both of which he managed to postpone , however , as the Doctor refused to change , having grown accustomed to being in his current incarnation , mirroring the First , Second and the Tenth Doctor ' s attitude towards the process . Furthermore , the Twelfth Doctor had also expressed he was sick of " always having to be someone else " ; reflecting how the Doctor has become tired of regeneration , having changed many times . The episode also shows the events leading to ' s regeneration into , with the male Master being mortally wounded by his female successor , and he in turn seemingly killing her , presenting how ( unlike the Doctor who has teamed up with his past and future incarnations and has gotten along with each incarnation he ' s encountered ) the Master rarely works with any of his other incarnations as he would eventually double - cross himself . Having displayed how the Master had regenerated into Missy , the episode marks the last appearance of John Simm as the " Harold Saxon " incarnation of the Master in his natural stream of events . Missy ' s fate , and as a whole the Master ' s fate , is unknown , and with Michelle Gomez ' s announcement that she was stepping down from the role " The Doctor Falls " marks her last appearance as Missy . The finale also shows that , while Time Lord s don ' t retain conscious memory of meeting their past or future incarnations , it is possible for their subconscious to retain certain thoughts and ideas . Notably , the Master had a hand in creating this branch of Cybermen , and though Missy didn ' t remember this , she was inspired to create her own army out of dead humans back in Series 8 . Missy ' s existence presented as a time loop ; if the Doctor had not chosen this ship to test her newfound goodness , she would not have been able to give her past self help to escape or mortally wound him to ensure he regenerated into her . As such , if Missy was not around , the Doctor would not have met Clara Oswald . The story featured several connections to the 1966 serial " The Tenth Planet " , including a story featuring human s from Mondas , and featured appearances by the Cybermen from said planet . Most notably , the episode featured the unexpected return of the First Doctor , now portrayed by David Bradley , in a scene set during the events of " The Tenth Planet " itself , the first time an incarnation of the Doctor from the classic series has appeared since the series was revived in 2005 ( excluding the mini - episodes " Time Crash " and " The Night of the Doctor " and the use of archive footage ) . Bradley had previously portrayed William Hartnell in the docudrama " An Adventure in Space and Time " . The episode explained that the Cybermen take on different appearances due to " parallel evolution " ; even though the Cybermen are descended from Mondasians , they came into existence in different parts of the universe . Synopsis . As he struggles to resist regenerating , the Twelfth Doctor prepares to make a last stand against the ever growing army of Cybermen . However , with Bill still a Cyberman , and gradually turning to her old wicked ways as reminds her of who she used to be , can the Doctor convince his old friend to finally be good before he falls ? Plot . The episode opens to a group of farmer s , adults and children , on Floor 0507 facing against the prototypes from Floor 1056 , dubbed " scarecrows " , shooting them down by night to then restrain them on wooden crosses by day . A school child is out in the field one morning when a shuttlepod blasts through the ground , crash landing near her . From the rubble , a Cyberman walks out carrying an unconscious Doctor . Sometime earlier , the Doctor awakes on top of the hospital , now restrained in a wheelchair , soon recalling how he was subdued by and . The Master and Missy dance and flirt , with him asking if she ' s his next incarnation ; Missy guesses she is as she can ' t remember what caused her to regenerate . The Master is stunned : " I ' m going to turn into a woman , and you can ' t remember it happening ? " Missy wonders if she is a woman ; the Master confirms it . Though the Master doubts it , the Doctor begins deducing what he ' s been up to since he vanished while blasting Rassilon with his life energy . Upon getting back to Gallifrey , the Time Lords , grateful for the Master ' s help in preventing Rassilon from executing The Final Sanction , properly restored his body . With that done , the Time Lords kicked him off Gallifrey . However , the Master stole a TARDIS to go back into the universe ; so he considers it a mutual being kicked out . After that , the Master landed on the colony ship , lived like a king and killed people at his leisure . However , the colonists eventually overthrew him and the Master attempted to flee . However , as his TARDIS was on the last level , too close to the event horizon , it burned out his dematerialisation circuit and left him stranded . " You never could drive could you ? " the Doctor asks . Both the Master and Missy are insulted ; she asks her earlier self if he has any requests as to how to torture the Doctor . They taunt their old friend by telling him of their plan of the Cybermen converting all the human s on the ship . They mockingly call the Doctor " granddad " , reminding him that Bill is now a Cyberman . The Doctor tells them that after all this time , if they still think they ' re winning when he ' s in the room , they ' re missing something obvious . Hearing the Cybermen advancing , Missy looks over the ledge and quakes in horror ; the Cybermen are coming for them . The Master is confused , as these Cybermen are primitive and shouldn ' t even be attempting to convert non - humans . The Doctor explains that when he was knocked down by Missy , he altered the signal of the Cybermen so they would convert two - hearted beings as well , hence why they are now focusing on the Time Lord ' s presence . The Masters panic , Missy frantically using her sonic umbrella to lock a metal door to hold back advancing Cybermen while the Master uses his laser screwdriver to destroy advancing Cybermen . The Doctor brags that he is the only one who is able to stop so many Cybermen at once . Realising this , a conflicted Missy knocks the Master out and frees the Doctor from his restraints . The Doctor starts wondering which side she is on to which she admits her indecisiveness as she is confused and her other half is unconscious . The Doctor uses his sonic screwdriver to contact Nardole , who reveals he has commandeered a shuttlecraft , lands near the roof to help escape , but the Doctor is grabbed and electrified by a Cyberman before he boards . Missy tries to save him using her other self ' s laser screwdriver but Bill , in her cyber form , intervenes first , destroying the Cyberman with a blaster based on her head . Missy and the Master try to convince Nardole to abandon the Doctor " The Doctor ' s dead ; told me to say he always hated you . " they both say . However , Bill prevents the shuttle from leaving , grabbing the ladders until they rescue him . They escape to Floor 0507 , where time moves slower . They find themselves on a solar farm , the Master deducing such by the holographic sky , where some of the humans and a large number of children protect themselves from the early Cybermen prototypes from Operation Exodus . Nardole approaches the girl , declaring they will need her help . They spend two weeks there while the Doctor recovers from his injuries . Bill awakes in the barn , unsure why the villagers are scared of her , concerned why she can ' t see the Doctor . When given a mirror by a child , she becomes horrified to discover she was converted into a Cyberman . The girl goes to run but bumps into the Doctor who thanks her for being kind to Bill , offering her a jelly baby as she leaves . The Doctor has somewhat recovered , though he still has a scar from where he was hit by the Master . Trying to console Bill , she gradually realises that though she thinks she is human , she is still a Mondasian Cyberman in appearance . She grows angry , the Doctor backing away as Bill accidentally triggers the blaster on her head , igniting the door on the barn , causing an explosion . Nardole , who has been preparing the town for the oncoming Cybermen despite one women saying he has been working them too hard , passively tells the farmers not to worry ; they have an upcoming war to focus on . Bill sheds a tear when she realises the humans are frightened of her , and the Doctor wipes it away , noting it unusual . The Master tells the Doctor that he and Missy have been working on something , and pauses briefly to mock Bill , chastising the Doctor for still referring to her as a female and taunts how he hated the time he had to spend with Bill as " Razor " . He stops because Bill claims he is not upsetting her , though she cries beneath her mask when he leaves . The Doctor finds it odd she is still able to shed tears . While traversing after the Master , the Doctor struggles to walk , limping heavily . He briefly stumbles against a tree , regeneration energy attempting to trickle from his hand . Wanting to not worry Bill , he draws up a stick and carries onwards but Bill is still distraught that the Doctor can ' t fix her current condition , the Doctor responding " where ' s there ' s tears ; there ' s hope . " They soon reach the middle of a forest , just after the Master and Missy theorize they can ' t retain their memories as their timelines are out of sync . Missy briefly displays empathy for Bill ' s condition , something the Master finds disgusting . Missy reveals she has discovered a camouflaged lift in the nearby forest , which she suggests they can escape to the bridge , using her sonic umbrella to call it . However , the Doctor declares that there will no doubt be a Cyberman in the lift waiting to find their floor , as the lift was taken to the bottom by them previously . Understanding this , Bill orders them to stand aside , the Doctor convincing the two Masters to do so . The three Time Lords prepare behind Bill , drawing their respective devices . As guessed , the lift brings up an advanced Cyberman from the lower floor , Bill speedily firing on it with her cyber blaster , the Master following likewise with his laser screwdriver as the Doctor and Missy use their sonic devices to slow its advance with a barrier . After several seconds , they disable it . The Doctor warns that ( through the Cybernet ) they will now have much more time to plan , given they now know what floor they reside on , so they must prepare for a battle . The Doctor returns to the village , revealing the alarm they now hear is the Cybermen ' s warning from the lower floors . Using a computer , Nardole discovers that the floor below this one has many fuel pipes that he can detonate as weaponry against the Cybermen , briefly testing such by blowing up a wind mill , stunning the villagers ; the Doctor remarks that they can use such to confuse the Cybermen and make them believe they are stronger than them . The Doctor finds a conduit to another solar farm on a higher floor that can be used to evacuate the children , having Bill blast it open , knowing this is a fight they will likely lose . Meanwhile , the Master and Missy decide to leave and plan to find the Master ' s TARDIS at the lowest floor , though the Master reveals he broke his TARDIS . Missy convinces her younger self to always keep a dematerialisation circuit on hand . She recalls the time a woman shoved her against her a wall to convince her to carry the device on her at all times . While recalling the story she shoves the Master against the wall , revealing herself was the one to convince the Master to carry the circuit . The Master hints to her that he is feeling sexual feelings for her , but Missy tells him it ' s very wrong . Night falls , the Doctor standing guard outside the house . Inside , a woman attempts to flirt with Nardole as he works on his computer , only to turn around and shoot at Bill , falsely thinking her a hostile Cyberman . She leaves distraught , going outside to the Doctor . The first wave arrives , Nardole and a girl preparing to combat them , successfully tricking them that an apple was capable of destroy an entire group of them . They retreat to the house , now understanding the Cybermen will likely return to outright destroy them next time rather than merely capture them for conversion . Meanwhile , the Doctor notices the two Masters trying to leave and runs after them . He pleads for them to be by his side to help . He gives an emotional and passionate speech on why he helps people , since it isn ' t easy or always going to work , it is just the right thing to do , as saving people would just be kind . The Master ridicules the idea , saying that he didn ' t listen to a word the Doctor said . However Missy was somewhat moved by the Doctor ' s speech , agreeing being the Doctor ' s friend was what she always wanted . However , after briefly grabbing each other ' s hand , she sides with her predecessor . At the lift , Missy tricks the Master into dancing with her and fatally stabs him , forcing his next regeneration , though she makes the wound " precise " so that the Master will have enough time to reach his TARDIS before regenerating . Gradually dying , the Master compliments her , glad they haven ' t lost their touch . After helping him into the elevator , Missy announces she will return to help the Doctor , turning to walk away as her predecessor shouts her to not go . Missy tells her past self this is where all the scheming , killing and egomania has led them : standing with the Doctor . Unable to accept that his future self will side with the Doctor , the Master draws and fires his laser screwdriver at full blast , causing Missy to collapse on the ground , fatally wounded . He claims the strike has disabled her regeneration , commenting that it is the perfect ending , with them both shooting themselves in the back . They both laugh as the Master descends in the lift and Missy seemingly dies . An initial wave of Cybermen arrive , but using Nardole ' s tricks with the explosives , they are able to make the humans appear more powerful , forcing the Cybermen to retreat and develop a new plan , giving the humans more time . Back at the house , and against Nardole ' s protests , the Doctor downloads the plans for the floor into his sonic screwdriver and sends him to help evacuate the children , intending to stay alone to fight the Cybermen . Nardole resists , having deduced the Doctor is going to commit suicide by detonating the entire floor in a last ditch attempt to destroy as many Cybermen as possible . The pair argue over who really should die , Nardole reasoning he can ' t given how he was before meeting the Doctor even though the Doctor tries to reason that he should stay as he is already dying . The Doctor eventually convinces Nardole that helping the children will be his penance for the crimes he committed before they met , as he is the stronger of the pair . Nardole jokes he will name a farm after him . Bill also insists on staying with the Doctor despite Nardole trying to tell her otherwise . As he leaves with the humans , Nardole admits that he will never be able to find the words for Bill and the Doctor ' s sacrifice . With all the humans evacuated , the Doctor and Bill prepare for a last stand , each deciding to charge into opposite ends of the forest . Bill says one last goodbye to the Doctor , even joking briefly about her sexuality , assuring him she had still retained her humanity . They face the oncoming wave . The Doctor ignites several of the Cybermen , listing the numerous times he has defeated them while doing so . However , he is inevitably surrounded and receives a full strike from one Cyberman ' s laser beam . He declares he is the Doctor but the Cybermen retort they have no need for a doctor anymore , firing at him again . Falling to his knees , he prepares to ignite the floor but is struck again , the blast proving fatal enough that his body attempts to regenerate . Refusing to give in , he holds it back and ignites all the pipes below the floor , engulfing it all in a wave of destruction , destroying all the Cybermen . Above on floor 0502 , Nardole waits outside of one of the lifts , hoping the Doctor and Bill will return however , the children convince him to move on and focus on living with them now . Back downstairs , the floor is now a wasteland scattered with destroyed Cybermen . Bill , barely functioning , finds the Doctor severely wounded . She mourns over the Doctor ' s body , but suddenly finds herself out of the Cyberman suit , seemingly human . She looks up and sees Heather ( from " The Pilot " ) who found her by her tears and changed her into a being like Heather . To prove to Bill that she isn ' t dead , Heather kisses her , after which they take the Doctor ' s body to the TARDIS , and Heather , as the Pilot , sets the controls for the TARDIS heading to a new location , while offering Bill to live out a different life , travelling the universe with her . Before leaving , Bill sheds a tear on the Doctor , but does not wipe it away , saying " Where there ' s tears , there ' s hope . " She walks over to Heather and the pair of them walk out of the TARDIS into space , off to travel the universe . The Doctor ' s wounds heal as he dreams of Bill and Nardole , yelling for him . He then dreams Rose Tyler , Martha Jones , Captain Jack Harkness , Donna Noble , Madame Vastra , Jenny Flint , Sarah Jane Smith , Amy Pond , Clara Oswald and River Song calling out his name . Twitching , the Doctor then dreams Missy saying his name and he awakes , gasping for air . Seeing he ' s begun regenerating , a confused Doctor mumbles some of the last words of his other incarnations . Yelling " No ! " with all his might , the Doctor suppresses the complete regeneration . " I can ' t go on always being somebody else " the Doctor cries out as the TARDIS lands . He tells his TARDIS that it doesn ' t matter where it ' s taken him ; he won ' t listen to whatever kind of lesson that it ' s trying to teach him . The Doctor steps outside into an arctic landscape . Out in the snow , yet again his regeneration attempts to start . The Doctor forces back screaming and stops the regeneration by shoving his fists into the snow , again stating he will not change . Suddenly , in the distance hears a voice stating the same words of not changing , finding the idea ridiculous . The Doctor calls out , asking for the person to identify themselves . The stranger asks for the Doctor ' s identity , which he confirms . The stranger replies that while the Doctor may be " a " Doctor , he is " " the " Doctor . The original , you might say " . Much to the Doctor ' s shock and surprise the stranger is revealed to be his first incarnation . Home video releases . DVD releases . " to be added " Blu - ray releases . " to be added " Digital releases . " to be added "