Previously before Dark Water/ Death in Heaven we hadn't seen The Master since David Tennant's farewell episode's. John Simm was the previous Master and his take was unbalanced as his version's body was dying, thanks to Lucy Saxon. We saw him save The Doctor's life and fight against Rassilon and disappearing back into the time war. Now we know that his body was too unstable due to him becoming Skeletor. The Master's body was apparently too damaged for him to regenerate. After disappearing within the Time War, The Master wasn't seen again until Peter Capald's debut series. This time he was now a female with Michelle Gomez taking over from John Simm. Missy was revealed to be the woman in the shop and the one who had brought the Doctor and Clara together. Throughout the series, Missy was seen watching the Doctor and Clara over the course of the episodes before the big reveal. Once again Missy was stopped and had seemed to have been killed. How wrong are we? The Master always comes back.
Missy will be appearing in Doctor Who series 9's opening two episodes. Not only that but Claire Higgins will also be appearing. The last time we saw Claire Higgins was in Night of the Doctor where Paul Mcgann's Doctor regenerated into the War Doctor.
Could we see something familiar with how The Master became female? Was Claire Higgins Ohilia involved in helping The Master survive his/her Simm incarnation by drinking a Elixir.