We've collected together some theories from the writers of The Gallifrey Times, which you can see below - but who will be right? Will anyone be right?
Ben (Video & Digital Media)
It's obvious, isn't it? She's a Timelord. She clearly knows the Doctor and has been following him for a while. She must have escaped the Gallifrey just before the Doctors hid it and kept a track on him. But which Timelord? I don't think they'd bring back the Rani just yet, but it must be someone high up if she has control of Cybermen and dead people. This leads me to believe that Missy is indeed... Rassilon's Mother! Think about it. Rassilon was obsessed with immortality in The Five Doctors, maybe he inherited that from his Mother. We've already seen her briefly, standing beside her son in Last of the Time Lords and now we know why the Doctor hated Rassilon quite so much. All this and Rassilon’s throwaway line in The Five Doctors, ‘My mother is going to be so mad.’ which was sadly edited out of all versions of the episode. So there you are, mystery solved. If she's not Rassilon's Mother, I'll eat my fez.
Owen (Instagram & News)
'Doctor Who?' More like 'Missy Who?' - That's my guess, Missy is a interpretation of the Doctor, the depths of darkness in the Doctor that have formed to battle the new Doctor, to see who he really is, and how his companions react in certain situations. A test for a new face. Like 'The Dream Lord', 'The Gatekeeper of the Nethersphere' is a side of the Doctor that wasn't meant emerge, a side of the Doctor that has gone wild on power and hunger. The Twelfth Doctor has hinted towards his face before, but maybe he chose 'this face' to help him remember how The Tenth Doctor managed to do a heroic act in 'The Fires of Pompeii' - The face has been chosen to heroically battle against Missy (the darkness in himself) to test himself and those around him.
Halloween feels like the right day to think about Missy, with an appropriate shudder at the shivery way she has appeared in the background of several of the 12th Doctor episodes. It feels clear she has until this point been designed to be a mystery to get us all thinking. Well for me I only really ever had one thought, the appearance and warped slyness of her manner makes me think of the Doctor’s nemesis the Master. By name alone this could work but the decadent antiquated clothes, deranged unnatural looking eyes, and evil tone of voice all in all make me think many fans wish for a major role to be played by a female may to some extent be (masterfully) granted...
So here is my theory on the mysterious 'Missy', and it has altered several times: she is a splintered, twisted version of Clara. This appears to be the prevailing idea, especially after the Next Time trailer for Dark Water and I can't help but begin to agree. Firstly is Missy's referring to The Doctor as 'my boyfriend'. Aside from the obvious choice of River, who else would view The Doctor as their boyfriend? Clara is the only other character who would take that viewpoint, given her attraction to him during her time with Eleven, which is specifically the era when she was splintered in his time stream. This is the perfect time for one of her copies to take a life of its own. Secondly, Missy states she has or had 'chosen well' when referring to Clara in Flatline. If this is a rogue copy of her, indeed she would compliment her original version's choice to jump in The Doctor's time stream and led her to where she is now. There is a distinct creepiness when thinking of Missy as Clara. I can't shake that scary thought.
Body swap. That’s why Clara’s being so mean to the Doctor in the Dark Water trailer. So we can take both that and the Missy we’ve seen so far into account. Another thing, Steven Moffat said we would find out why the Doctor has that face this series, we still don’t know yet. So what if Missy collects dead people for the Time Lords? Then their bodies can be reused each time one of them regenerates. That’s how that face was frowned; it belonged to somebody else before the Doctor. Now Missy has run out of regenerations, and the only person who can give her more, is the Doctor!
Louis (Assistant Editor)
The identity of Missy is clearly quite a big deal - enough for scenes to be chopped from the preview copy of Dark Water. Despite these cut scenes, given the clues in Dark Water, it's quite obvious she's
And that's all we have time for. Who do you think Missy is? Do you agree with any of our writers, or do you have another theory? Leave a comment below!