Dark Water ( TV story ) Dark Water was the eleventh episode of the eighth series of " Doctor Who " produced by BBC Wales . It saw the return of the Cybermen and , and the Twelfth Doctor ' s first encounter with both . The events of the episode centred around the sudden and unexpected physical death of Danny Pink after a fatal accident , his transition into an existence beyond his body and the effect his bodily demise had on Clara Oswald . The story also explored the concept of an engineered afterlife , and revealed the identity of the victim unintentionally killed by Danny when he was still a soldier . " Dark Water " showed an important aspect of the Time Lord ' s regeneration process that had been mentioned before , but never seen on screen : the possibility for a change of gender to occur . Missy , a mysterious figure throughout the series , was revealed to be a female incarnation of the Master , showing for the first time in the history of the series a Time Lord who had been portrayed by male actors , now being portrayed by a female actor . This was also the first encounter between the Doctor and the Master since " The End of Time " , before each had changed into their next incarnations . However , it was not revealed when the previously male Master had regenerated , nor how she had escaped the pocket dimension that held Gallifrey . This would later be revealed in the Series 10 story , " The Doctor Falls " . " Dark Water " , and its follow - up episode " Death in Heaven " , were shown in cinemas in 3D as a two - night event on 15 and 16 September as a run - up to prepare for series 9 . The screening also featured a prequel scene to the ninth series . Synopsis . In the mysterious world of the Nethersphere , plans have been drawn up . " Death is not an end , " promises the sinister organisation known only as 3W – but , as the Doctor and Clara discover , you might wish it was . Plot . Clara is ready to confess to Danny the adventures she ' s been having with the Doctor , despite telling him she wasn ' t . She ' s about to tell him over the phone , when Danny steps out into the road and is killed by an oncoming car . Unable to deal with her grief , Clara calls the Doctor for help with the intention that he ' ll change events . The Doctor picks up Clara asking her where she wants to go , almost immediately sensing something is wrong . She asks the Doctor to take her to a volcano , all while collecting up the TARDIS key s that are hidden in the console room . After the Doctor sets the destination , Clara uses a sleep patch on him . The Doctor seemingly wakes on a volcanic planet , and Clara tells him what ' s happened and that she is holding the seven TARDIS keys hostage . Clara then reveals that she knows lava can destroy them and if the Doctor doesn ' t let her try to save Danny she ' ll throw them all into the crater in order to prevent the Doctor from ever re - entering the TARDIS , proving that she ' s serious by throwing one straight away . The Doctor point - blank refuses to save Danny since his death is part of her personal timeline , changing that event will lead to a paradox . He tries to take control of the situation by goading her to throw another key in the lava . Clara then throws all but one in , and when the Doctor still won ' t help she throws the last in before suddenly being overcome by the enormity of what she ' s done . The Doctor then reveals that she didn ' t actually knock him to sleep ( the two are still in the console room ) , and this has been a telepathic test to see how far she ' d be willing to go to be with Danny again . Seeing the extremity of her desire to see him , despite his fury at her betrayal of him , the Doctor agrees to do everything he can and connects her to the TARDIS ' telepathic circuits , as her time stream ' s connected to Danny ' s . The TARDIS takes them to wherever she thinks Danny now is , even speculating about travelling to the afterlife , since most cultures have a concept of it . Danny wakes - up in the Nethersphere , and is greeted by Seb , who informs him of his death . The TARDIS has taken the Doctor and Clara to the 3W , where they see skeletons seated in watery graves . They ' re greeted by Missy . Stating that he clearly didn ' t receive the formal advance materials , she kiss es the Doctor , and claims to be a Mobile Intelligence Systems Interface . Missy lets the Doctor feel her heart , evoking a reaction of quiet surprise from the Doctor . In the Nethersphere , Seb asks Danny if he ' s ever killed someone , due to a request from someone Danny could have killed in the army . Remembering his " bad day " , the child Danny accidentally killed is revealed to him . Chang reveals the dark water to the Doctor and Clara . When submerged , only organic matter can be seen – the skeletons are inside something else , hidden by the water . Danny meets with the child , who runs away when Danny tries reaching out to him . He and Seb hear a man screaming , which Seb explains to mean he left his body to science . Chang then explains to the Doctor and Clara that the 3W was established after a discovery from television static , that their founder , Dr Skarosa , translated to be distant voices . Believing them to be the voices of the dead , Skarosa isolated some of them . Chang plays a recording of the voice that inspired 3W ' s founding : “ Don ' t cremate me ” . Chang tells them the dead are still conscious , and aware of everything that happens to their body . The Doctor mocks such an idea . Seb is explaining the same to Danny , who constantly feels cold because he ' s still connected to his body , which is being kept in a cold place . The Doctor states that the dead don ' t come back , and Chang establishes a communication signal to the Nethersphere , and Clara is able to speak to Danny , with Seb ' s assistance . The Doctor tells Clara to ask Danny questions only to which would he know the answer . Missy activates the tanks , and the skeletons stand . When Chang and the Doctor arrive , Missy reveals she was only pretending to be an android , and kills Chang . As the tanks begin to empty , the Cybermen are slowly revealed . Clara asks Danny to name the restaurant of their first date – he can ' t remember . Missy shows the Doctor the Nethersphere , which is a Matrix data slice housing minds of the deceased in edited forms , while their bodies are used for Cyber - conversion . The Doctor knows the Nethersphere ( actually a small sphere within 3W ) which is containing the neural patterns is actually Gallifreyan technology , and Missy reveals that she is indeed a Time Lord , or rather a Time " Lady " as she prefers to be called . The Doctor asks her which Time Lady she is – she ' s the one he " left for dead " , without expecting her to " find [ her ] way back " . The Doctor runs out of the 3W , which is St Paul ' s Cathedral . Clara asks Danny more information about her and tells him that if he is Danny , she is determined to find him in the netherworld and threatens to hang up if he says " I love you " one more time instead of answering her questions . Danny tells Clara she must continue her life and not follow him ; he repeats the same words for the last time and she disconnects the communication signal . Seb gives Danny the option to delete himself , which would relieve him from the surge of emotional trauma from his call with Clara . Back in 3W , Clara turns around to see a fully - revealed Cyberman in the water tank . The Cybermen activate , and begin marching down the steps of St Paul ' s Cathedral . The Doctor yells at civilians to run away , but he ' s dismissed as an angry Scotsman . The Doctor demands that Missy tell him who she truly is , and Missy reveals that her name is short for " Mistress " as she couldn ' t keep calling herself by her previous title . . . the Master . The Doctor initially reacts with disbelief that quickly turns to horror when he realises she is telling the truth and his old nemesis has returned . In the Nethersphere , Danny is on the verge of disconnecting himself , and sees the child he killed reflected on the screen of the iPad he holds .