[Mild SPOILERS for those not caught up on Doctor Who season 9 ahead.]

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Doctor Who season 9 has so far been composed of two-part episodic narratives - something that will continue with its upcoming fifth and sixth episode, "The Girl Who Died" and "The Woman Who Lived", respectively. "The Girl Who Died" will in turn pick up with the current Doctor (Peter Capaldi) and his companion Clara (Jenna Coleman) on another wild adventure in space and time, while at the same time introducing a special guest star to the Doctor Who universe: Game of Thrones' Arya Stark herself, Maisie Williams.

Current Doctor Who head writer/show-runner Steven Moffat has already nixed various fan theories about Williams' character - ranging from the idea that she is the Doctor's long-missing daughter re-generated, to the claim that she might be a fresh re-generation of the Doctor's wife, River Song (who we now know will be played by Alex Kingston again in the Who 2015 Christmas special). Williams is instead playing a new character altogether, though clearly one of importance to this new story about the Doctor.

The above Doctor Who clip blends footage from "The Girl Who Died" with interviews featuring Capaldi and Coleman discussing the episode. For more on that subject, you should read the episode's official logline, below:

Captured by Vikings, the Doctor and Clara must help protect their village from Space Warriors from the future; the Mire. Outnumbered and outgunned their fate seems inevitable. So why is the Doctor preoccupied with a single Viking girl?

That "Viking girl" in question is Ashildre (Williams), and the reason behind the Doctor's interest in this character remains an enigma, for the time being. "The Girl Who Died" was co-written by Moffat and Jamie Mathieson - the latter of whom also penned the Doctor Who season 8 episodes "Flatline" (which made our countdown of underrated Doctor Who episodes) and "Mummy on the Orient Express" - and Williams said the following (in a statement released by the BBC) about her audition experience for the role of Ashildre

“I didn’t know much about it, but knew they were introducing a new character to work closely with the Doctor. I’d got through the second episode and absolutely loved it! I was going to do a tape but ran out of time because I was in America shooting another film, so my agent worked really hard and sent over lots of clips and videos – they liked them and gave me the role.”

For more from Williams on fans' reaction to her landing a Doctor Who role, check out the video below:

Interestingly, whereas both halves of the Doctor Who season 9 two-part opener ("The Magician's Apprentice" and "The Witch's Familiar") and the following two-part episode narrative ("Under the Lake" and "Before the Flood") were penned solely by the same writer - Steven Moffat and Toby Whithouse, respectively - that won't be the case with this season's third two-parter. "The Woman Who Lived" will instead be written by Torchwood alum Catherine Tregenna - the first female Doctor Who writer since Moffat became head writer, as it were. However, both episodes will have the same director, in the form of Edward Bazalgette (Poldark).

Moffat's two-part Doctor Who season 9 opener was criticized for retreading thematic territory from season 8 (in addition to adding a controversial twist to a key part of the show's mythos - see the link below), while Whithouse's follow-up two-parter arguably offered a better and more creative, genre-blending Doctor Who story on its own terms. Those two-episode adventures maintained a consistent authorial tone throughout, but it remains to be seen if the three writers involved with the next two-parter aim for a similar achievement - or, if the Doctor and Clara's first encounter with Ashildre ends up being very different than the second half of their story together.

NEXT: Doctor Who Writer Toby Whithouse Discusses the 'Sonic Shades'

Doctor Who season 9 continues with "The Girl Who Died" @ 9 p.m. on BBC America. For an additional sneak peek of the episode, check out the clip below:

Source: BBC America