Battle of Floor 0507 The Battle of Floor 0507 was a skirmish between the Twelfth Doctor and the residents of Floor 0507 against the Cybermen invading from Floor 1056 on a Mondasian colony ship . Initially ruled by , the Cybermen turned on him when the Doctor rewrote their definition of humanity , leading to the group fleeing to the upper floor while the Cybermen prepared to conquer the entire ship , the final stage of Operation Exodus . The Cybermen held a significant advantage as they were further away from a black hole , meaning years for them was mere days for the Doctor and the others on the solar farm , allowing them more preparation time . The skirmish was eventually ended when the Doctor , having had Nardole evacuate the majority of the residents to floor 0502 , used his sonic screwdriver to ignite the floor , destroying all Cybermen present at the cost of forcing him to regenerate . ( TV : " The Doctor Falls " ) History . Origins . Due to the colony ship being sucked into the orbit of a black hole , 20 members of the 50 member crew on board went to floor 1056 to reverse the thrusters . However , the time dilation meant they aged much faster , several generations soon being spawned . At some point , crashed his TARDIS here and took control , eventually steering the residents down a path to convert themselves into cybernetic humanoids , and eventually a complete Cyberman . The patients would venture to the higher floors and capture the other residents for conversion . ( TV : " World Enough and Time " ) A group went to floor 0507 , but were repelled by the residents , being shot down daily . ( TV : " The Doctor Falls " ) Eventually , the Twelfth Doctor , Bill , Nardole and landed on the ship , finding the sole survivor on floor 0000 , Jorj , who was spared due to not being completely human . He shot Bill due to her being a human , the patients coming and taking her away . Bill was later kept under the Master ' s watch at the hospital ( under the guise of " Razor " ) until he had her converted into the first true Cyberman . The Doctor , Nardole and Missy followed after knocking Jorj out and figuring out the time dilation between the numerous floors . However , the Doctor was too late to save Bill and Missy joined the Master , siding against the Doctor as they gloated about the " genesis of the Cybermen " . ( TV : " World Enough and Time " ) The pair then captured the Doctor , knocking him out and taking him to the top of the hospital where they gloated about their victory . However , the Doctor revealed that he had changed the definition of humanity in the Cyber network , turning the army against the Master . After fending the initial group off with his Laser screwdriver , the Master was knocked out by Missy using her Sonic umbrella , who then freed the Doctor from his restraints . Nardole then arrived in a shuttlecraft , the group proceeding to use it to evacuate . However , the Doctor was electrocuted by a Cyberman , Bill ( as a Cyberman ) having to save him using her laser beam . She then forced the two Masters to take her and the Doctor with them . The shuttlecraft eventually crashed on floor 0507 . ( TV : " The Doctor Falls " ) Preparing for war . Over the next two weeks , Nardole took command of the village , having the residents prepare for the upcoming attack from the Cybermen , fortifying the town with sandbags . Missy and the Master took to locating the lifts on the level , eventually finding and revealing one to the Doctor and Bill . However , Missy accidentally called the lift to their level , forcing the four to fight off a highly advanced Cyberman , as years had passed for floor 1056 . Realising the Cybermen now knew where they were and would now have years to prepare an invasion while they would have only a day , the Doctor returned to the village to rally the residents for the battle , the Cybermen sending a warning in the form of an alarm in an effort to frighten them . Understanding they would need a way out , the Doctor had Bill blast a hold in the wall to an underground passage leading to the lifts while the Masters schemed to flee to the Master ' s TARDIS on floor 1056 . Nardole used a computer to hack into the fuel lines beneath the floor , enabling him to detonate them on command . The Doctor decided they would use such a tactic to make the Cybermen believe they had superior weapons so they would not attack beyond the first wave , at least for a while . Shortly before the Cybermen arrived , the two Masters revealed their plan to leave to the Doctor . Infuriated , the Doctor pursued them , proceeding to criticise the pair for their indifference and that he was staying to fight because it was " kind " and " right " . Although the Master refused to listen and left , Missy was moved by the Doctor ' s speech , considering siding with him . However , she sided with the Master , thanking the Doctor for trying to make her good . ( TV : " The Doctor Falls " ) The battle . The initial wave of Cybermen arrived , marching towards the town . However , they were met by Alit , who tossed an apple at them . Nardole , using his computer , ignited the fuel line beneath the platoon , blowing them up . The Master and Missy manoeuvred through the forest to the lift , witnessing the explosions in the distance , avoiding the Cybermen . Nardole proceeded to do destroy several of the Cybermen , the house remaining safe , the Cybermen soon retreating . Understanding they had little time before the Cybermen returned with their entire army , the Doctor downloaded Nardole ' s software into his sonic screwdriver and ( after a long argument ) convinced Nardole to go with the evacuating children to protect them . Bill also opted to stay with the Doctor , wishing to die defending the children rather than continue living as a Cyberman . In the forest , the Master and Missy successfully reached the lift . However , having changed her mind , Missy tricked her predecessor and stabbed him in the back , asserting she wanted to stand with the Doctor . This wound would force the Master ' s regeneration into Missy , though she made it precise so that he would have enough time to return to his TARDIS first . Helping the dying Master into the lift , she prepared to return to the main site of the battle . However , the Master struck her down with his laser screwdriver , professing he would refuse to let her help the Doctor . Laughing at their " perfect ending " , the Master descended in the lift as Missy appeared to die . By morning , Bill and the Doctor knew the rest of the Cyber - Army were imminent , sharing one last goodbye with Bill before she left . Alone , the Doctor reiterated the words his wife River Song once told him : " without hope , without witness , without reward . " The second wave arrived , the Doctor and Bill each charging into opposite ends of the forest , fighting off various types of Cybermen . As the Doctor destroyed numerous models of them , he shouted out the numerous occasions he had beaten them . Eventually , he was surrounded and struck down by one Cyberman ' s laser beam . Wearily declaring he was still the Doctor , the Cyberman rebuked him and fired again . As his body attempted to regenerate , the Doctor ignited the entire floor , destroying all of the Cybermen and mortally wounding himself in the process . ( TV : " The Doctor Falls " ) Aftermath . Safe on floor 0502 , Nardole stood outside the lift , wondering if the Doctor and Bill would return . The children convinced him to move on and focus on living with them . Nardole stated to the children that the Doctor ' s actions had only destroyed " most " of the Cybermen , but would buy them several years for Nardole to come up with a new plan . Below them on floor 0507 , the Doctor had become motionless after the explosion which had destroyed all the Cybermen but Bill . Bill was then confronted by the oil creature in the form of Heather , which had tracked Bill down due to leaving itself as residue in Bill ' s tears . It turned her into a creature like itself , and together they took the Doctor back to the TARDIS . Heather invited Bill along to explore the universe with her , and after bidding the Doctor farewell Bill and Heather left . After Bill and Heather ' s departure , the Doctor awakened and began to regenerate . ( TV : " The Doctor Falls " ) He eventually finished the process , regenerating into the Thirteenth Doctor . ( TV : " Twice Upon a Time " )