Although some fans of Doctor Who felt a little let down about the big reveal behind Game of Thrones' Maisie Williams on the series, others liked the surprise at the end of "The Girl Who Died."

Please note that the following contains spoilers for this week's episode of Doctor Who, and probably a few spoilers for next week, too.

In "The Girl Who Died," the Doctor realized that he should save people after remembering his 10th incarnation, who saved a man from Pompeii. That man, as fans of the series know, was portrayed by Peter Capaldi, who is now the actor behind the 12th Doctor. So the episode hinted that the Doctor chose that same fate for his most recent regeneration to remind him that it was OK to break the rules and save people from time to time.

So that's what he did: after Ashildr (Williams) died in this week's episode, the Doctor put a tiny chip into her forehead and brought her back to life.

But that wasn't without a cost: that little chip basically made Ashildr immortal, which is why the Doctor left behind a second chip for her, in case she found herself wandering the world alone, something the Doctor understands all too well.

In next week's episode, Ashildr appears again, and we see that time has changed and hardened her (and it's hard not to see Arya Stark in Williams' expressions). In a preview of next week's episode, "The Woman Who Lived," she tells the Doctor, "I don't need your help, Doctor. You need mine."

This week, the Doctor lands in the 1600s in England. Something referred to as "The Nightmare" stalks the streets of London and the Doctor must figure out what's going on with this thing and why it's showed up on Earth.

This preview also shows the Doctor asking Ashildr "what happened to you?" And the answer is what usually comes from those whose lives the Doctor has touched in some way. "You did, Doctor." Of course, Williams makes it sound sinister, and fans might wonder if we'll see her throughout the run of the season, rather than in just these two episodes.

Here's the official synopsis for "The Woman Who Lived:"

"England, 1651. The deadly Highwayman 'The Nightmare' and his sidekick stalk the dark streets of London. But when they find loot that's not of this world, they come face to face with The Doctor. Who is the Nightmare in league with? And can the Doctor avoid the hangman's noose and protect Earth from a devilish betrayal?"

Doctor Who airs Saturdays on BBC America.

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