The Girl Who Died ( TV story ) This episode introduces a new warrior alien race , known as the Mire ; much like Sontaran s , they revel in battle . A new immortal is introduced , Ashildr . It also marks one of the few mistakes that the Doctor has made when he ' s emotional . This story also once more shows how easily aliens were able to manipulate humans before they learned of the possibility of life beyond the stars ; to them any advanced technology is magic . The Mire leader posed as Odin , tricking the people into not fighting when his soldiers harvested fighters for sustenance . The story was notable for revealing the origins of the Twelfth Doctor ' s face : he had unknowingly taken on the likeness of Lobus Caecilius , a man whose life the Tenth Doctor had saved . This marked the first time " Doctor Who " had given an explanation for the Doctor being played by an actor who had previously played a different role in the series . Colin Baker , who first portrayed the Time Lord Maxil , later went on to portray the Sixth Doctor ; however , in this instance it was never explained in - universe why the Sixth Doctor had taken on Maxil ' s appearance , or if the likeness was deliberate . Synopsis . After adventure and a half in space , the Doctor and Clara are kidnapped by 9th century vikings . However , to make matters worse , hostile aliens have also arrived in the vikings ' village ; they are provoked into declaring war on the village by a stubborn girl . By the end of the adventure , the Doctor will learn where it was that he saw his own face before , and the reason why he chose it . Plot . Clara is floating in space , desperately calling the TARDIS for a pickup . The Twelfth Doctor answers , but says he ' s too busy at the moment to help as the TARDIS is under attack by the hostile aliens attacking the Velosian s . Clara then notices that something is in her spacesuit ; the Doctor suggests it ' s a Love Sprite , a parasite that eats brains from out of the mouth , hence the name . The Doctor points out it ' s because she spent too long in the spider mines . He then asks her to list the four most interesting stars she can see : two whisky - coloured stars below a blue one and a green wing - shaped nebula . Within moments of the Love Sprite getting too close to Clara ' s head , the Doctor materialises the TARDIS around her and takes off her helmet . Clara breathes heavily in relief . The Doctor chases the creature , squashing it under - foot . Clara wonders how things worked out on his end . The Doctor retorts he just saved an entire planet by transporting their attackers half - way across the galaxy and draining their weapons systems ; not to mention saving a school teacher from suffocating / having her brain eaten . The Doctor decides to land the TARDIS to clean his boot in the grass ; he steps outside into a forest , bracing himself against a tree as he wipes the Love Sprite off his boot . Clara wonders what ' s to stop the aliens from attacking again , to which the Doctor says " nothing . At least this time , they ' ll be ready for them . I ' m not actually the police , Clara ; that ' s just what it says on the box . " He explains that as time travellers , it ' s okay to make ripples , not tidal waves ; Clara laughs , calling him a tidal wave . Realising that was a jinx , he retorts not to say that . At that moment , they find themselves held at sword - point . The Doctor moans about not being in the mood for viking s , who surround them . The leader tells the Doctor that he and Clara are coming with them . Filled with his usual confidence / arrogance , the Doctor puts on his sonic sunglasses , gloating that what he wears on his face is technology more advanced than anything the human race will manage in the next nine million years . Unimpressed , the leader simply takes the sonic and breaks them in half . Seeing that he should have had a backup plan , the Doctor flatly tells Clara that they ' re going with the vikings . Two days later , the Doctor and Clara are dragged by the vikings back to their village , enchained . For the last two days , which was spent on a rowboat , the Doctor has been lying to Clara about having a plan , to keep her calm . However , Clara has travelled with him long enough to know when he ' s lying . The leader gifts a girl named Ashildr with the right half of the Doctor ' s sonic sunglasses ; she seems to think it ' s a weird eye patch . Clara wonders if the Doctor has a plan now , to which he says is the usual - " find the boss man , replace him " ; he recites Clarke ' s Law to Clara , who wonders " is it going to be the yo - yo again ? " To her surprise , she finds the Doctor has already freed himself of his cuffs using what he calls " magic " . The lead viking addresses his father , whom the Doctor takes to be the village leader . Tossing his yo - yo at the viking , the Doctor is met with blades pointed at him . The Doctor loudly declares that he ' s cross with the vikings and that he ' s very , very disappointed in them ; he tells them that he ' s taken human form to walk among them . When a villager asks for his identity , the Doctor tosses his yo - yo upwards , yelling " Surely , you would recognise the sign of Odin . " The vikings declare that the Doctor is not Odin and the yo - yo is not Odin ' s sign , to which he asks if they have actually met Odin and know what he looks like . As if responding to the Doctor ' s words , what seems to be Odin ' s face appears in the sky . Odin declares that the day of reward has come for the villagers ; the Doctor yells " Do not believe this impostor " as he fails at a yo - yo trick , embarrassing himself . Odin declares the best warriors will dine with him in Valhalla . Clara wonders if its really Odin , to which the Doctor says " he doesn ' t even have a yo - yo " - no , it ' s not Odin , just a better fake . Armoured aliens teleport down , and begin scanning the villagers . They teleport away the strongest warriors . The Doctor explains they ' re not invading , but harvesting ; children and the weak will be ignored . Outraged , Clara wants to stop them , but the Doctor tells her they need to avoid being chosen ( as this will let them escape ) . Ignoring him , Clara rushes over to Ashildr , whom she instructs on how to use the sonic sunglasses to unlock her cuffs . Unfortunately , the advanced tech is noticed , they are both teleported to a ship hidden behind Odin ' s projection . On board the ship , Clara notices that her cuffs are gone and that the warriors are impatient to meet Odin . The leader tries opening a door in front of them , succeeding only to be zapped into dust in the next room . A wall begins pushing everyone into the chamber , despite their best efforts to jam it with their blades . Clara and Ashildr manage to open the door on the other end of the chamber , barely escaping the next zap that reduces the other warriors to dust as well . On Earth , Ashildr ' s father , Einarr , notices that all the chosen went willingly to Valhalla , while another says he wouldn ' t due to fearing heights . Annoyed at their stupidity and superstitions , the Doctor tells them that homo sapiens are an intelligent species , so they should stop lying to themselves ; they just got raided . Einarr tells the " false Odin " to choose his words carefully , to which the Doctor admits that he lied , but " the big fella in the sky " lied too " because what ' s the one thing Gods never do ? Gods never actually show up ! " When the Doctor says he lost someone important , Einarr retorts that he did as well . Back on the ship , Clara and Ashildr wake to find themselves in what appears to be a factory . Ashildr wonders why they are still alive . " Odin " arrives with two aliens , saying it ' s because of the sonic sunglasses ; he examines them in his hand . He asks Clara to explain . Taking the Doctor ' s role , Clara says she ' s sorry for scaring the aliens , to which " Odin " denies . Clara knows he ' s examined the sunglasses and determined that they have from a civilization far more advanced the village , not to mention she ' s wearing a spacesuit . An alien brings " Odin " a vial of green liquid , to which Clara quips " time for your medicine ? " " Odin " calls it nectar , downing in a gulp ; it was made from the warriors ' adrenaline and testosterone ; Clara is puzzled as to why aliens travelled to Earth to " mash up " some vikings for " warrior juice " . She asks " Odin " why he played God to vikings , to which he says there ' s always some kind of " farmer " that " cattle " will respond to . Clara call " Odin ' a thief caught in the act , asking him to seek warriors elsewhere for his sustenance as " the universe is full of testosterone ; believe me , it ' s unbearable . " She then asks " Odin " if he really wants to start a war , seeming to make him consider leaving peacefully . However , Ashildr butts in , declaring revenge . " Odin " laughs , saying he was almost fooled into leaving as " words are the tools of cowards . " He tells them that ten of his warriors will attack tomorrow . Surprised " Odin " is being so idiotic , Clara asks for his reason . " Odin " says it ' s for " the joy of war " ; his species live for the battle . He then removes his hologram face , to show his joy . Ashildr is left shocked that she has declared war on a monster . Back in the village , the Doctor reads his 2000 Year Diary , learning the aliens are the Mire , who leave others alone if they get what they want ; they are one of the deadliest warrior races in the galaxy . Clara returns at that moment , explaining Ashildr ' s blunder . The Doctor tries explaining that the best option for the villagers is to run , since the Mire will give up on trying to kill them if they hide out for about a week . However , he fails due to their pride ; upon hearing a baby ' s cries , which the Doctor can understand as words , he decides to stay and teach the villagers basic combat . He nicknames them as he hates to waste time learning names . Unfortunately , they are too blundering or questioning to be properly trained , resulting in accidents . Clara tells the Doctor to stop playing soldier and start looking for what he ' s missing - how he ' s going to win - because he always finds it at the last minute . The Doctor comes across Ashildr , who is fighting a puppet of Odin . Ashildr explains she makes puppets and comes up with stories whenever the raiding parties head out , believing the right story will ensure their safety . She further elaborates about never really fitting in with boys or girls , due to the girls all thinking she ' s a boy and the boys all thinking she ' s just a girl . Her father " Chuckles " consoles her , to which the Doctor allows them privacy . However , he then notices " Lofty " is stealing the baby . Ashildr explains it ' s Lofty ' s child ; he takes her to the boathouse to see the fish when she won ' t settle ; the Doctor immediately realises why , calling for Clara as he rushes to the boathouse . The Doctor examines the buckets as Clara enters ; she wonders if he got his hand stuck in something again because he ' s yelling . The Doctor explains he ' s found what he ' s missing and that no - one told them they had " fire in the water " - electric eels ; telling Chuckles to inform everyone that bedtime is cancelled , the Doctor goes on to announce " " There ' s going to be a war tomorrow . This just in : we ' re going to win the Hell out of it ! " " They spend the entire night prepping for battle ; the Doctor tells the group that they should look happier than their enemies as its assures winning and to always walk briskly as it makes them moving targets . He also adds to act like they know their enemies ' plans , as sometimes , very rarely , they will be goaded into revealing them . Among the various items mentioned for the plan are anvils and the silver wiring from Clara ' s spacesuit . After the prep - work is done , the Doctor explains the plan - if they can get him a helmet from a Mire soldier , this entire thing is over ; they can mop up the rest with Ashildr ' s monstrosity . The moment it ' s unveiled , Clara points out it ' s " rubbish " , to which the Doctor smirks " I know " . The next day " Odin " arrives with some of his men , they enter a barn , where the Doctor , Clara and the villagers are all dancing and having fun . When Odin points out that it ' s time to fight , the Doctor says they decided to have a party and there ' s not a single weapon in the barn . " Odin " , desiring a fight , threatens to kill everyone as it wouldn ' t be the rest time the Mire caused a senseless slaughter of innocent and unarmed people . During this time , Lofty has been tossing rings on the Mire suits , failing at six ; the Mire are briefly startled . On the Doctor ' s cue , Chuckles startles a bucket of eels ; their electric charge is channelled into the barn by the wiring taken from Clara ' s spacesuit , rendering six of the Mire suits immobile . The villagers run out as the Doctor cues Chuckles to startle the next bucket , which turns an anvil hanging above the Mire into a magnet that takes their helmets and blasters . Yelling for the magnet to be turned off , the Doctor takes a helmet , while Clara takes a blaster to hold the Mire at bay . The Doctor quickly gives the helmet to Ashildr , who uses the visual link to trick them into thinking a puppet of a sea monster is a real one attacking them . All but " Odin " teleport back to the ship . Ending the ruse , the Doctor shows " Odin " the recording of this embarrassment on Clara ' s phone , which has been made funnier by adding " The Benny Hill Theme " ; he threatens to upload it to the Galactic Hub ( and thus ruin the Mire ' s reputation ) if they don ' t leave peacefully . " Odin " threatens the Doctor ' s actions will not go unpunished , but is teleported back to his ship by the Doctor , who hacked the system . Without any further conflict , the Mire leave the Earth ; the Doctor will likely keep a copy of their humiliation to keep them from any more senseless fights . The villagers rejoice in their victory . However , the Doctor discovers that using the Mire helmet has drained Ashildr ' s heart , leaving her dead ; he had not foreseen it would take such a toll . The Doctor is left brooding about the loss , with Clara trying to comfort him , saying he couldn ' t save her . He snaps back , saying he can do anything , but the Laws of Time prevent him from doing so . Looking at his reflection , the Doctor suddenly remembers back to when he first saw it , wondering once more " who frowned me this face ? " Suddenly , the memory comes back to him ; Donna Noble encouraged him to always try to at least save someone even in a fixed point , and he saved Lobus Caecilius ' family from Pompeii ' s destruction . He tells Clara that the reason his subconscious chose this face when he regenerated was to remind him to always save someone , no matter how impossible or wrong it seemed . The Doctor then yells to the sky : " I ' m the Doctor , and I save people . And if anyone happens to be listening , and you ' ve got any kind of a problem with that , to hell with you ! " Rushing back to the barn , the Doctor fiddles with the helmet and pulls out a chip . He puts on Ashildr ' s forehead and activates it , bringing her back to life ; it ' s the medical kit for the Mire soldiers . The Doctor gives her father a second chip , telling him it ' s for whoever she wants ; he explains to Clara that the kit would likely keep repairing her , preventing Ashildr from dying . The second chip is to prevent her from being alone for eternity . Returning to the TARDIS , the Doctor is left wondering if he did the right thing ; when he ' s emotional , he makes mistakes . Clara assures him everything will be fine , because what he did was born of good intentions . Brooding again , the Doctor says , " Time will tell , it always does . " However , he then realises that his actions have turned Ashildr into a hybrid . Ashildr is then seen in a montage of time passing her by , but with age never affecting her . As the screen pulls into her face , she is shown to have stopped smiling , her smile being replaced with a grim stare . . . Story notes . Filming locations . " to be added " Production errors . " to be added " Home video releases . DVD releases . " The Girl Who Died " was released on DVD as part of " Doctor Who : Series 9 , Part 1 " on November 2 in region 2 and November 3 in region 1 . Blu - ray releases . " to be added "