The Doctors Arch enemy the Master. Back on Gallifrey they were friends but the Master was driven insane and tried to take over the universe! To stop her she was locked in vault where she has been trying to turn good. After helping the Doctor a couple of times he thinks she can be trusted however when she meets her previous incarnation how long will she stay good for? #DoctorWho #DrWho #TheMaster #Missy #Master #DoctorWhoSeries10