My Master/Doctor Theory
What if the doctor and the master were actually married?
Since when do you care about the doctor?
She said just one of it is wrong, so there’s the possibility that the doctor was female before Gallifrey fell. So if he was female and Missy male and the two were best friends, well… They wouldn’t be the first best friends who fell in love.
Missy had a daughter.
Why would the doctor gave her this if that girl wasn’t his daughter, too? Didn’t he say that he knew the master was insane since they were children? Why give it the daughter of a friend that he knew he’d go insane sooner or later, if he didn’t care about that child?
It’s proven that the doctor had a daughter, since Susan Foreman is his grandchild. Yes, she never called him “grandmother” but I think gallifreyan children are used to it that their relatives change their gender in time.
Means that they could’ve had a daughter together theoretically.
So, if all I’m saying is true what there are questions:
Why aren’t they together anymore?
Why did they become arch nemesis?
You are the Master and you and your wife have children, then you fight because your wife thinks you’re insane since you took a look into the time vortex. She tries to convince you to get help but stubborn like you are, you can’t see where the problem is.
Gallifrey is under attack. You both get killed and regenerate. You don’t know what your wife looks like anymore and can’t find her (because you’re looking for a female obviously). You hear a rumor that she calls herself the doctor now and run away, minutes before the doctor’s about to push the button to destroy the planet. You escape Gallifrey as well.
Your wife, or now husband, is on the run with your only grand-daughter, your children and everyone you know are dead. You start to hate the doctor.
How devastating must it be to know that your partner has taken everything away from you you loved? To know that your partner just run away. Without you. That he didn’t care enough to take you with him as well?
And that’s the reason why Missy likes Clara but actually wants to destroy her.
She’s her husband’s new girlfriend (or at least that’s how she sees it). She is jealous. She wants her partner and her daughter back.