Oxygen ( TV story ) Most notably , in this episode , saving Bill robs the Doctor of his sight , rendering the Twelfth Doctor , potentially , permanently blind . This shows the risks he often places himself in , in order to save his friends , but also the danger in which he might be leaving Earth , should he not return , alive and in good health . " Oxygen " represents a tipping point in the St Luke ' s vault arc , as the Doctor finally faces the consequences of not having taken his vow seriously . Nardole joins the Doctor and Bill on this adventure , for the first time since " The Pilot " . Synopsis . The Twelfth Doctor , Bill and Nardole investigate a strange space station , but are interrupted by walking dead in spacesuits . . . will they make it out alive ? And how much does air actually cost ? Plot . On the outer hull of the space station , Chasm Forge , workers Ivan and Ellie , working a technologically - advanced smart suits make their way to the top of the space station to make repairs . Ellie attempts to communicate to Ivan , with whom she is romantically involved , using her comms system , admitting to him that she is now ready to have a child with him , but he can ' t hear her due to interference with the communications systems . Ellie examines her air tank to discover that she is running low on oxygen and is required to purchase more . From behind her , two figures start walking toward her , also wearing suits but without their helmets and the humans wearing the suits are obviously dead . Ellie turns to see them advancing on her and she screams , but Ivan can ' t hear anything . Just as he finishes his repairs , Ivan turns to look behind him and sees the two figures along with a now dead , helmet - less Ellie advancing on him and he screams . On Earth , the Doctor is in the middle of a lecture , which is supposed to be about crop rotation , but instead he makes it all about space . After the lecture , Nardole approaches the Doctor and calls him out on his desire to go back into space . When working on the vault , he voices his concern that the Doctor has plans to take another unauthorised trip , but the Doctor rebuffs that , stating that he is still on Earth guarding the vault . Later in the TARDIS , the Doctor is telling Bill about the possibilities that exist with exploring space ; he suggests that Bill select a destination for a trip , but then himself sets course to investigate a distress signal . At the point , Nardole arrives and insists that the Doctor remain on Earth and guard the vault . He presents a fluid link component he took from the TARDIS after one of the Doctor ' s lectures , under the assumption that it would render the TARDIS immobile . However , this was a lie on the Doctor ' s part as he then suddenly sets the TARDIS engines in flight , much to Nardole ' s surprise and chagrin , but to Bill ' s delight . The TARDIS materialises in a corridor on the space station and the Doctor , Bill and a very - angry Nardole emerge . The Doctor expands the TARDIS ' air shell so that they can explore . Bill is amazed by the depths of space when looking out the space station ' s window , while Nardole is still moaning about the Doctor breaking his oath again . The trio then discover a man in a suit standing in the middle of the repair bay . Upon examining him , they discover the mean to be dead , but Nardole finds his air field is still up , meaning he didn ' t suffocate ; Bill finds it rather distressing that the mechanical suit is keeping the dead man propped upright . The Doctor examines the computer logs and discovers the station was declared non - profitable after a majority of it ' s workers were killed . The three proceed further into the station and discover a suit with no operator doing work . Suddenly , a computer ( whom Nardole remembers as an ex - girlfriend called Velma ) states that there has never been oxygen in the station and the unauthorised oxygen from the TARDIS has been detected and will be expelled . The Doctor , Bill and Nardole race back to the TARDIS when the section starts decompressing the expanded air shell from the it . The Doctor seals the section off using the sonic screwdriver , but it leaves them unable to return to the TARDIS . A comms unit suddenly engages on the computer , and the voice on the other end introduces himself as Tasker . While the Doctor , Bill and Nardole are distracted , the suit propping up the dead man becomes active and starts advancing towards to trio . The Doctor tries to disable it with his sonic screwdriver , but it ' s magnetised out of his hand by the suit and crushed , disabling the suit as a result . Nardole looks outside an sees that the deceased workers a being operated by the suits and are advancing on them from the outer hull . The Doctor deduces that the oxygen is contained in the suits , so in order to survive , they put on the suits present in the repair bay . While escaping from the Smartsuits pursuing them , the TARDIS crew are rescued by Tasker , Ivan and other survivors on the station , Abby and Dahh - Ren . The crew tells the Doctor that the suits are property of the company which has turned access to oxygen into profit , and that the suits have received instructions to ' deactivate their organic components ' . All other crew were killed by an electric shock to their nerve systems , rendering them zombies . The crew make plans to retreat across the station ' s hull and escape to an uncompleted section of the station that isn ' t present in their station ' s mapping . Suddenly , the suits break into the section where the crew are hiding and kill Tasker with the electric discharge by touching him . The remaining survivors retreat to an airlock at the end of the section , all putting on helmets to protect themselves from the vacuum . During the process of decompression , the suit Bill took from the repair bay begins to malfunction , taking off Bill ' s helmet of it ' s own accord . The Doctor attempts to to release Bill ' s helmet from the suit ' s grip , but to no avail ; he warns Bill that she is about to be exposed to the vacuum and to breath normally . The airlock opens and Bill loses consciousness when exposed to the vacuum . She briefly reawakens to find herself being walked across the hull by the Doctor , without his helmet and Ivan and Abby shooting advancing suits , before falling unconscious again . Bill awakens alone in an empty section of the station . She looks up the hallway to see the suits outside the open door but not entering . Bill is approached by Nardole and Ivan , who reveal that the suits can ' t get into the section because it ' s a new area that isn ' t in their mapping system . Bill asks about the Doctor and Nardole tells her that he gave her his helmet and walked her to safety , but it did cost him . He tells her he ' s in Section 12 , a statement which the suits register and begin trying to locate . Bill finds the Doctor sat alone in the section . He stands to face her and reveals that walking in the vacuum unprotected has blinded him . He ensures her that the condition is temporary and that his sight can be restored on his return to the TARDIS . The crew regroup and the Doctor makes plans on how to get them out alive , but Abby doesn ' t believe his capability , due to his inability to save Tasker and threatens him . At that point , the suits log Section 12 into their mapping system and come in , killing Dahh - Ren . Abby attempts to hold them off , but the crew end up fleeing . Just before making it to the next section , Bill ' s suit malfunctions again , magnetising itself to the floor and rendering her immobile . Know that there is no way of getting Bill to the next section , the Doctor leaves her behind while the others escape and the suits approach her . Bill makes an appeal to her mum while the suits deliver the electrical discharge and seemingly kill her . The remaining survivors arrive at the station ' s power room , where the Doctor highlights on the suits operation being heavily established by a capitalist attitude . The Doctor claims that he is attempting to redirect the flow of water cooling the generators to convert it into oxygen , but instead connects the generators to their suit ' s life signs , meaning that if they die , the generators will overheat and explode . The Doctor insists that the suits be let it , seemingly as a grand statement about the inevitable downfall of capitalism , and Ivan reluctantly complies . As the suits advance and are about to kill them , the Doctor declares that their deaths would be expensive and the suits stop . The suits analyse the generators and conclude that the would be a greater loss for the company if the crew were to die and the station were to explode , so the suits remove their oxygen tanks and give them to the survivors . The Doctor also re - engages Bill ' s oxygen tank and Bill revives , her suit ' s battery having too weak an electric charge to prove fatal . Back onboard the TARDIS , Nardole restores the Doctor ' s eyesight , and the Doctor gives Abby and Ivan the option of what they wish to do . They wish to be taken to head office to make a complaint about the company and the events that transpired on Chasm Forge , to which the Doctor complies . Later , back at the university , the Doctor tells Bill that the after effects of Abby and Ivan ' s complaint was the catalyst for the eventual downfall of space capitalism . After Bill leaves , Nardole emerges from the TARDIS , still furious at the Doctor ' s reckless behaviour . He berates the Doctor for endangering himself in a selfish gesture and points out to him that he knows the stakes of leaving the vault unattended , posing the possibility of him returning injured or sick or even dead , that there would be no - one to guard the vault effectively then . The Doctor refuses to look at him , and as Nardole continues to berate him , he rises and removes his glasses , claiming he ' can ' t look at anything , ever again ' . He ' s still blind . . . Story notes . Production errors . " to be added " Home video releases . DVD releases . " to be added " Blu - ray releases . " to be added " Digital releases . " to be added "