My issue with the "twist" ending here is the same issue I always have with Moffat. He dragged it out (within the space of the episode) far too long and by the time it was finally revealed I just didn't care.
I don't think if there weren't speculations on the Internet anyone would need such rush to reveal everything. What are we hurrying for? Sometimes a mystery is just some revelation whose time hasn't come yet. I wouldn't be that mystified about who Missy was if it weren't for the speculation here. More importantly, the big reveal was for
the Doctor, which worked wonderfully. (I usually hate mysteries, and this seemed like a mystery-lite to me.)
Clara, who probably knows the most about the Doctor and his life when compared to most of the modern companions, still chooses to betray him and try to kill him (dream state or not)?
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The whole point of the companions is that they allegedly "make him a better man" but his impact on them (and all the people he helps) is also significant. If we are to take this episode (and, really, series 8 so far) the argument can be made that whatever likeability Clara had with Eleven has been completely undone by her time with Twelve/Capaldi. She's a douchebag now.
To me that was just Clara showing that she is a flawed human like she ought to be. In grave and unexpected moment of distress, she was driven by emotion like many of us would be. And she made a grave mistake, one very grave mistake, which she immediately realised. Like most people she is dangerous around a machine of immense power like the TARDIS. It would have been the Doctor's fault for not being more careful with
any of his companions if they went rogue, particularly unwittingly. No matter what they've been through or what wonderful people they are, the sheer scale of what they can do – to themselves, to the Doctor, and to the universe – is incomprehensible to most of us.
That actually undoes the complaint that the TTOTD somehow made her the Doctor's pivotal superhero. Pivotal yes, superhero no. Circumstances and the very same emotional stubbornness she displayed here made her jump without thinking and subject her other selves to deadly encounters with the Doctor to save his life over and over. As remarkable as that is, it hardly makes her an unerring person who has some remarkable self-control. If she had such self-control, or any self-control at all, the Doctor would probably be dead, because a moment of honest contemplation on what saving him meant would have scared the shit out of anyone.
The Doctor has always travelled with a great deal of questionable people (TDOTD shouldn't make Clara a special companion). Right now he's hanging with someone who performs vigilante capital punishment by eating criminals alive. Yesterday I watched The Romans and the Doctor and his companions were directly responsible for a bunch of people dying, setting the entire Rome on fire and Vicki nearly wrecked the entire timeline on a whim after being told not to repeatedly. Granted, she's new to time travel, but that hardly compares to being faced with the sudden death of the one you love the most.
Come on, isn't every SciFi character allowed their "I don't care if history itself comes unravelled" moment?
After likely being made aware of all the things the Doctor went through with Rose, Mickey, Jackie, Martha and her family, Jack, Donna and her family and all the other one-shot companions? After everything Clara herself went through with Eleven? All throughout his life as the Impossible Girl schtick?
It was multiple parallel versions of Clara – ones that have been confirmed to have gaping holes in their memory – who visited his timeline all over. This Clara only saw a glimpse of his previous incarnations during that scene in TTOTD. Or maybe she knows anyway, but there was no on-screen evidence to that.
Finally, as I've thought on it after a night's rest, I'm not altogether convinced "Missy" really is The Master. It could well be Moffat, in a singular fit of brilliance, is actually trolling us and that this is a red herring cliffhanger. I'd be quite impressed if that turns out to be the case but I'm also well-prepared after the past three seasons for it to just be more "Gee whiz cool!" crap from Moffat.
After the self-repairing droid scene and her overall plan, I don't see much chance for that. She's the Mistress, putting on Simm's act mot à mot. After watching, I was almost convinced Simm's Master had also kissed the Doctor at some point.
The doors open when you snap your fingers.
Yet another plot point Moffat introduces that he then later ignores. But let's not forget, he's clever!
This isn't the first occasion where he couldn't open the door. Scratch that, that wasn't an occasion where he couldn't open the door
at all. That could only be a discussion of Clara's clarity of mind. Which she obviously didn't have. At all.