A bird-like spaceship hurtles through an asteroid belt, pursued by Daleks. They shoot, the ship explodes and the pilot finds herself unconscious on the floor of a strange ship, in front of a hawk-faced man holding takeaway coffee.
She is Journey Blue, a soldier in the galactic resistance, and her brother was her co-pilot. She pulls a gun on the hawk-faced man, who says he is the Doctor, and tries to force him to take her to her command ship. After insisting on some basic manners, he does.
It seems the command ship, named Aristotle, is a former hospital, useless now since the Daleks don’t leave any wounded people behind. There is but one patient, a Dalek in need of a Doctor.
Meanwhile, at Coal Hill School, former soldier Danny Pink has started work as a math teacher. It seems he has some turmoil in his past (tears in the classroom) and when he’s introduced to Clara, he makes such a nervous hash of being friendly she has to ask him out for a drink just to break the ice.
And then someone else arrives with a drink for Clara. It’s the Doctor and his coffee. And he has a question:
Back in the Aristotle, it seems the Dalek has been injured in battle and has somehow become good. So good it wishes to destroy its own race, but it has been injured and requires medical assistance. The plan is to miniaturize a team—the Doctor, Clara, Journey and two soldiers, Ross and Gretchen—and go inside the Dalek (through the eyestalk) to help it recover enough to be of use in the war.
Once inside, the Doctor points out the cortex vault, the electronic memory filter that deletes any evidence that contradicts the Dalek’s skewed worldview. The cortex vault is how the Daleks keep their hatred pure and fresh. Ross tries to shoot a zip wire so they can access lower levels, but this triggers the Dalek’s robot antibodies, and he is vaporized for protein. The Doctor leads everyone to the Dalek’s waste tube, or gullet, the place where Ross’s broken-down protein has ended up. It’s a slide with a gunge tank at the bottom and they’re all going down.
Luckily the way out is via some hot tubes, so they’re all nice and dry by the time the Doctor finds out what is up with Rusty the Dalek. It is suffering from radiation poisoning and has become susceptible to the beauty of creation, and this has changed its outlook. The Doctor fixes the radiation leak, allowing Rusty to restore itself. Sadly, this means restoring the old Dalek sensibilities and Rusty commences shooting everyone outside, and notifying the Dalek fleet send boarding Daleks to come and attack the hospital ship. This is not a good moment.
For the Doctor, this just confirms his feeling that the Daleks are rotten through and through, which irks Clara into slapping his face. Journey starts to lay out explosives while Clara leads the Doctor towards a different conclusion, that there may actually be some spark of redemption inside all Daleks.
So, the Doctor sends Clara and Journey up to the cortex vault to try and reintroduce those memories that first encouraged Rusty to abandon its conditioning. And he goes to speak to Rusty face to face. The boarding Daleks are inside the Aristotle and slicing their way through everyone aboard, so there’s no time for climbing. Gretchen sets up another zip wire, knowing it will trigger the antibodies and lead to her death. Journey and Clara fly up to the cortex vault and the Doctor heads off to talk to Rusty, meanwhile Gretchen finds herself taking tea with Missy in heaven (remember Missy from “Deep Breath”?).
Clara works out how to relaunch the good memories in the cortex vault while Journey tries to hold back the antibodies, while the Doctor admits that it’s the Daleks that have given him his moral framework. He was just running, then he went to Skaro, and realized he had to be everything they were not. With Clara’s final boost to its memories, Rusty re-boots, re-experiencing the epiphany that changed its mind. And the Doctor then fuses his mind with Rusty’s, to triumphantly seal the goodness in.
Except, there’s a problem. The Dalek sees all the beauty in the universe, and is humbled by it, but also sees the burning hatred in the Doctor’s soul for all things Dalek. A hatred so potent it leads Rusty to attack the other Daleks, killing them all. Not that this is any comfort to the Doctor, especially as, in a final twist of the knife, Rusty refers to the Doctor as “a good Dalek.”
In a moment of poor timing, considering all that has just happened, Journey asks if she can accompany the Doctor on his travels, but he turns her down. Clearly his need to be un-Daleky extends to preferring not to associate with soldiers (although his time with UNIT may suggest otherwise).
Back in school, face to face with Danny Pink and remembering Journey Blue, Clara decides that she does not share the Doctor’s view on solders. Not all of them, at any rate.
Next week: “Robot of Sherwood”