In Missy's final episode, she and the Master (John Simm) dance together and taunt the captive Doctor as they celebrate the genesis of the Cybermen, but Missy is conflicted about her loyalties, especially when the Cybermen start coming for them.

As the Cybermen close in on the group, Missy and her past self plot their escape together in the Master's TARDIS while the Doctor prepares to defend the colonists and makes an emotional plea to the good person that Missy was becoming. Ever more torn between good and evil, between her devilish past and her complex friendship with the Doctor, Missy finds herself with a difficult and deadly choice to make.