Tonight's episode clinches it: Doctor Who is doing a much more ambitious character arc than it's done in years, even as the show's "mystery" storytelling is drastically scaled back. Even with a few stumbles here and there, this is really major. You have to applaud the ambition, and a lot of the execution. Spoilers ahead…
In previous years, under both Russell T. Davies and Steven Moffat, Doctor Who has mostly focused on mysteries and plot-based arcs, from Bad Wolf and Harold Saxon to the Silence and the Impossible Girl. Companions have gotten a bit of development here and there, including an arc of Rose Tyler realizing that the Doctor had previous companions and she will eventually be replaced. And Amy and Rory trying to decide whether to keep traveling with the Doctor or put down roots. And the Doctor has had bits of development here and there, including slowly getting over his Time War trauma and then getting "too big" and having to disappear.
But I'm hard-pressed to think of a season of Doctor Who that's been so clearly built around a character arc as season eight, in which the central question is all about whether Clara is going to be another one of the Doctor's good soldiers... or whether she's going to be more of an officer, like the Doctor himself. And meanwhile, the season's big plot mystery, that of Missy and Paradise, is being deliberately kept on the back burner. Which is great.
We started the season with the Doctor questioning whether he's a good man, and Clara questioning whether she wants to keep traveling with someone who's so much meaner than the Matt Smith incarnation. And then Clara meets the Doctor as a frightened child, and we see a parallel between the formative experience that turned the Doctor into a monster-fighter and the similar experience that turned Danny Pink into a soldier. Clara's caught between the Doctor and Danny, when the Doctor endangers their school with his high-handedness.
Then to prove to Clara that he's not a monster, the Doctor first forces her to make an impossible choice on her own (kill a creature inside the Moon, or risk killing Earth) and then shows her a situation where his manipulativeness is the only way to save people.
So there's a general theme of the Doctor being a lying, cruel bastard, Clara not being entirely on board with it and seeing herself as his conscience, and the Doctor having contempt for soldiers while also turning people around him into soldiers. And Clara learning to understand, and accept, the Doctor. Most of all, Clara confronting a dark part of herself that's not so different from the Doctor, which is pretty interesting in itself.
Invasion from Flatland
In tonight's episode, "Flatline," all of this takes another huge step forward and a lot of the season's themes really seem to "gel." The Doctor gets trapped inside his shrinking TARDIS for most of the story, and Clara is forced to step up and become a surrogate Doctor — which puts her in the position of making the kind of tough calls the Doctor routinely makes.
She's investigating a mysterious case of disappearances on a council estate (and how they're related to the shrinking time machine), and she has to make the best possible use of the "local knowledge," particularly a young graffiti artist named Rigsy. And then later, she's corralled a small group of people who were doing community service, plus their incredibly unpleasant supervisor Fenton, and she has to establish herself as their leader. And, basically, lie to them.
Clara discovers that she's actually pretty good at messing with people, and that she makes a decent "Doctor," at least in that department. (She still needs the Doctor to build a gadget for her, and later to use the TARDIS against the episode's monsters, once she tricks them into channeling power into it.) Meanwhile, Clara is also lying to her boyfriend Danny about her decision to keep traveling with the Doctor (and to the Doctor about Danny's feelings on this.)
Basically, Clara is a way better liar than she had acknowledged — and as the Doctor says, lying is a crucial survival skill, but it's also a really bad habit.
None of this is particularly subtle, but that's okay — Doctor Who often doesn't do subtle, and this is all in the service of exploring a character flaw of Clara's, as well as showing how she has a lot more going for her than even she realizes. It's sort of cute that the episode about two-dimensional monsters is the one where Clara takes a huge step towards being more three-dimensional herself.
Plus we've seen Doctor Who do the thing of "the Doctor is callous and mean and his innocent companions don't understand," as far back as the Hartnell era. ("The Massacre" comes to mind, but so does "The Daleks.") We much more seldom see the Doctor's callousness explored — and then see the companion realizing that she's really the same, deep down.
Totally evil monsters
For the second week in a row, Doctor Who gives us monsters that really are just evil. (As opposed to misunderstood, or misguided.) The villains of "Flatline" are the denizens of a two-dimensional universe, trying to invade our 3D world. Their only knowledge of humans is based on our footprints and other contact with flat surfaces, so they start trying to pull us into their 2D world. (And they shrink the TARDIS by feeding off its external dimensions.) Later, these creatures (the Boneless?) start trying to study us, creating 2D images of human skin and a human nervous system.
Eventually, the Boneless (terrible name) become more aggressive, creating pseudo-3D "people" out of the skins of the people they captured earlier, and flattening doorhandles and things so that their victims can't escape. Eventually, they trap Clara and her crew in a train tunnel, where the TARDIS gets run over. (And there's a hilarious sequence where the Doctor has to move the tiny TARDIS out of the path of an oncoming train by sticking his hand through the doors and moving it Thing-style. Only to celebrate too soon.)
The great thing, this time around, is that the Doctor and Clara make a serious, good-faith effort at communicating with the Monsters from Flatland. After all, these creatures could just be trying to reach out to us, and might not understand that they're killing us by squishing us. So the Doctor and Clara use pure mathematics, via sound waves — and the monsters respond first with the jacket number of the guy they just killed, and then the jacket number of the guy they're going to kill next.
The fact that the monsters are basically nasty makes this all a lot more straightforward, like it did with the mummy, and it's just a matter of outwitting them. Clara rams a train into them — and Rigsy nearly sacrifices his life, but she sacrifices her hairband instead, in a cute scene. And then she gets Rigsy to draw a flattened door handle that looks so realistic, the creatures pour all their dimensional energy into it to un-flatten it — thus giving power to the TARDIS, so the Doctor can banish them back to their dimension.
And once again, there's a class dimension to all of this — the monsters are free to prey upon the people in the Council Estate because they're living in public housing and the authorities don't care. People like Rigsy have their creativity ignored and suppressed by completely awful authority figures like Fenton, who's basically an unthinking jackass who keeps trying to undermine Clara. In an especially dark twist, most of the nice people in the story die, while the loathsome Fenton survives.
In the end, the Doctor gets to emerge from the TARDIS just in time to make one of his trademark shouty speeches about how he's the Doctor and he fights monsters. Maybe he's overcomepnsating, after Clara did such a good job of "being" him — in any case, this speech is probably my least favorite part of the episode, since I'd sort of thought we were over that now.
What does Missy want with Clara?
So this episode — and this season, in general — are all about Clara recognizing that she's not just the Doctor's conscience, she's actually just as bad (or good) a game-player as he is. But the end of the episode does tie that character arc into the season's fairly slender plot mystery — that of Missy "Misdemeanor," the lady in charge of Heaven who's spying on the Doctor. She's observing Clara's progress, and seems very pleased with her choice:
As we learned in the season opener, Missy was the woman in the shop who gave Clara the Doctor's phone number so she could call him about her wifi troubles back in "The Bells of St. John." And she's apparently been grooming Clara for... something. Something that requires Clara to be more than just a standard companion, more assertive and ruthless.
Does Missy's plan for Clara have anything to do with the fact that Clara went inside the Doctor's timeline and became a kind of uber-companion to all of his previous incarnations, dying again and again? I'm guessing probably not — for one thing, that hasn't been mentioned at all this season, and Clara doesn't seem to remember it.
For another, I wonder if that even happened at all — the Doctor didn't die at Trenzalore the way he was "supposed" to, which means there's no future tomb on that planet, and thus no timeline for Clara to step inside. That whole business may have been erased when Matt Smith managed to regenerate into Peter Capaldi. (The other option is that the Doctor will, at some point in his future, go to Trenzalore AGAIN and get involved in yet another centuries-spanning war on that planet, which will result in his irrevocable death. But I highly doubt it.)
Anyway, I'm cautiously optimistic to see where this is all going — I hope that a season of character development for Clara doesn't get turned at the last minute into a widget of some sort, as the "Missy" plot comes to fruition. As long as that doesn't happen, this is very good stuff — a real solid character-based storyline in which the villainous masterplan is wrapped up with the process of Clara growing up and becoming more of a real person.
Some people have been saying that Capaldi is a welcome change but the writing on the show hasn't changed that much — but I'd say that's been disproved at this point.