Craig here. It gives me great pleasure to introduce a new guest blogger – @thommck !
Missy Who?
Missy is this series’ big enigma. Who is she, where does she come from, is she a new or returning character?

This blog is me putting forward my bit of bonkers on answering some of those questions. I’ll try to support it with only facts from within the episodes we have seen. It definitely does not contain any spoilers and is purely my speculation. I’ll be really interested on your thoughts and urge you to put forward your own theories on Missy.

The Facts
We actually don’t know a lot about Missy. All we’ve seen so far is as follows – a female dressed like she is from Victorian England despite a more modern spiky bracelet.

• Deep Breath – The clockwork cyborg, Half-Face Man, was impaled and died in London in the Victorian times. Missy welcomed Half-Face Man into the Promised Land/Heaven, looking out on a lush garden. She claimed the Doctor is her boyfriend and that she’d “keep his accent”
• Into The Dalek – Gretchen Carlisle was killed while miniaturised inside a Dalek. She then appeared at a table in what looks like an early 20th Century tea room, where Missy offered her some tea.
• Robots of Sherwood – Alien robots in the Middle Ages were trying to reach a planet called the Promised Land, although this may be different place to where Missy is.
• The Caretaker – In a white room, we met Missy’s assistant (companion?) Seb, who took care of the recently deceased PCSO, Matthew. Missy appeared but was “too busy” to see him.
• Flatline – Missy was watching Clara remotely, with what looked like a 21st Century iPad

Top 10 Theories
I tried to make a list of all the current popular theories but I’ve heard so many it became almost infinite! Here is a rough top 10 amalgamation (in no particular order)

1. The Master
2. Another Timelord/Timelady (in or out of Gallifrey, Romana, Rani, Scintilla)
3. A computer/data bank/imagination (CAL, e-Space)
4. Wife/girlfriend/descendant/ancestor to the Doctor (Susan, River Song, Jenny)
5. A previous companion (Clara, Adric)
6. A future Doctor/Valeyard
7. Robot/clone/doppelganger/replicant/shapeshifter/zygon
8. An old “villain” (e.g. Miss Mercy Hartigan, Tasha Lem, Madame Kovarian)
9. A dinosaur 😉
10. Something new!

“The Woman In The Shop”, who gave Clara the TARDIS telephone number (Bells of St John), is also a popular theory but that could be any of the people above (well except maybe number 9!)
My Speculation
I am putting my money on number 2, a Timelady trapped in another universe.

We have seen/visited other universes and dimensions before in Doctor Who and they have just recently been highlighted in the episode, Flatline, which contained creatures beyond human perception. I think this is enough evidence to point to Missy being in a parallel/pocket/bubble universe/etc. rather than a digital memory bank (i.e CAL).

I had a quick look in to the history of parallel universes in the show as it gets a bit confusing trying to just remember it!

The Tenth Doctor said that there were “billions of parallel universes all stacked up against each other.The Void is the space in between, containing absolutely nothing.” (TV:Army of Ghosts) … At one point, travel between parallels was made relatively simple by the Time Lords, but, according to the Tenth Doctor, travel to parallel universes became almost completely impossible after the Last Great Time War, and could only happen under extraordinary circumstances. (TV: Rise of the Cybermen) … tardis.wikia.com/wiki/Parallel_universe

The iPad Missy was seen using felt really odd to me. It is such an object of this time, right down to the protective cover it had. This makes me think Missy is now on 21st Century Earth but perhaps has the ability to time travel/dimension hop/phase. This can explain how she got Half-Faced Man from the Victorian era in Deep Breath as well as Gretchen from our future. Miniaturisation may well play a part as that has also been heavily referenced this year. Perhaps the ability to travel between universes is easier if you’re small!

This leads me to believe that Missy has to be a Timelady, one we haven’t seen on screen before. She has a “companion”, Seb, and “Heaven” could possibly be her TARDIS. She was made Guardian of the Nethersphere (a.k.a. Heaven, The Promised Land) by the Time Council as a punishment for a crime. She is on her last regeneration and would interrogate the dead to try and discover the secrets of immortality.

Since The Day of The Doctor we know that Gallifrey is still out there, vanished from our universe but still reachable through a crack. I’m not sure if Missy is on Gallifrey. I’m more inclined to believe she is in Void space or a parallel universe.

Her motive for pushing Clara and the Doctor together isn’t very clear to me at the moment. The easy option is that it was the Doctor who condemned her to her position as Guardian and so she is looking for revenge. The more bonkers version is that the Doctor is her boyfriend so she wants to kill him to bring him to Heaven. She is nudging Clara into a Doctor-type role so someone can relieve the Doctor of his duty, permanently!