Doctor Who is nearly at the halfway point of its tenth season and so far the series has only been delivering hints of the overarching storyline at the end of most every episode. That has pertained primarily to the idea of the vault the Doctor and Nardole have taken an oath (well, maybe just the Doctor) to watch over while spending the better part of half a century lecturing at a university. It's literally a sort of mystery box intended to build tension and generate intrigue in the background while Pearl Mackie's Bill Potts learns her way around the TARDIS and the sort of stakes her mentor is playing with during all of his timey wimey jaunts through space and time. So far, season 10 has managed to provide a hasty Doctor Who education for Bill, readying her and the audience for a more serialized back half of the season focused more on the occupant of the vault and the Doctor's pending regeneration.

Last week took the question of the vault in a new direction. After weeks of ominous glances at the Gallifreyan-looking doors and the very loud, powerful banging that made it seem as though whatever or whoever was inside was definitely making the world a better place by being on the other side of those doors, the Doctor offered another side of the story. Bringing some Chinese food, he entered the vault; greeting its occupant as someone he was not just familiar with, but also comfortable enough to have a chat and risk opening the doors. The Time Lord's actions weren't exactly strange considering all that he's seen and done in all his iterations, but it did add a welcome wrinkle to the season's big mystery.

But this is still Doctor Who and even with seven episodes (and a Christmas special) left to go in the season, there's still time to spend an hour in a wildly familiar situation. That being: the Doctor and his companion find themselves trapped in a structure – a mining space station this time – trying to rescue a small group of survivors while also solving the mystery of what strange affliction, alien life form, technology run amok, etc. managed to wipe out the rest of the crew. This time, the tried and true Whovian formula mixes undead space miners with a fantastical kind of futuristic space suit presumed to be the cause of the interstellar zombification of the miners.

As it turns out, the zombification of the workers is superficial – the workers really are dead; the suits that killed them on behalf of a faceless corporation's bottom line are just carrying them around. It's all part of a corporate ecosystem that exploits the workers by charging them for the air they breathe and then killing them shortly before their replacements arrive. The whole affair is reminiscent of an incredibly dark Black Mirror episode, and makes for a compelling twist on what could have been a rote zombies in space scenario, but in fact becomes exponentially darker when it is discovered just how little human life is worth to the corporation in question and the lengths to which it will go in service of the almighty dollar.

The twist is the second time this season that Doctor Who has taken capitalism to task right there in the text of the hour. The first being 'Thin Ice' in which the lives of the poor were considered fair game – or fish food, really – in an effort to line the pockets of a wealthy businessman who stood to profit off the excrement of a giant river monster. It's not hard to see just what the episodes are getting at in depicting miners callously worked to death and the lives of some underprivileged citizens literally reduced to… well, you know. Both were largely about institutions operating in bad faith, aiming to exploit others specifically for monetary gain. While the theme made for interesting not-quite subtext for both episodes, it also underlined the anti-authoritarian element of the Doctor himself, something that feels even more present in the Peter Capaldi version of the character.

That's especially true this season, as the Doctor has been operating under the pretense of being shackled to a day job of sorts, one that he's growing to resent as it's keeping him from doing the thing that he loves. In the case of 'Oxygen', the Doctor misses traveling around in space. He misses it so much, one of his lectures becomes about the dangers of space travel and just how hostile interplanetary travel is – a clever way of setting up the particular environmental (or lack there of) stakes of the episode itself. Framing the Doctor's yearning for adventure and freedom with his obligation to watch over the vault and make sure its doors never open – which is an intriguing contradiction to the end of last week's episode – is a clever way of serving the needs of the season's mysterious overarching storyline with the recurring theme of institutions operating in bad faith.

This time, though, it's the Doctor who pays the price. After Bill's space suit malfunctions, he gives her his helmet and winds up blind as a result of prolonged exposure to the vacuum of space. It's a narrative obstacle that doesn't really trip the Doctor up too much – he still manages to use the mining corporation's money-grubbing tendencies against it to win the day and save some of the survivors – but the Doctor's lack of sight isn't immediately wiped away with typical Doctor Who-style "I've got a gadget that can fix that" storytelling. Well, the Doctor insists he has a gadget that can repair the damage done to his eyes, and even presents himself to Bill as having had his sight restored. It's not until the episode's closing moments that the reveals to Nardole (and the audience), that the damage has not been reversed.

The Doctor's sightlessness itself seems symbolic in a way, a symptom of his efforts against the societal ills that can erupt from capitalism run amok. But it also leads nicely into the idea that this is the end of an iteration of the Time Lord. His body has seemingly experienced irreparable damage, suggesting regeneration is not too far behind. Whether or not Doctor Who plans to continue this story throughout the rest of the season is a question that will have to wait until next week to be answered, but it does create an interesting wrinkle in the familiar story of the Doctor's journey toward inhabiting a new body.

Next: Doctor Who Season 10: What’s in the Vault?

Doctor Who continues next Saturday with 'Extremis' @9pm on BBC America.