What clues does this new Doctor Who picture hold about the Christmas special?

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1 Bill’s dress sense

Ever since we learned that Bill would be returning for the Christmas special, we've been speculating about the details. How? When? And in what form? Could this outfit provide some clues?

The black bomber jacket and stripy top are rarely seen items from Bill's wardrobe but she was wearing them both in World Enough and Time, the penultimate episode of series ten, in some of the last scenes before she was converted into a Cyberman.

Later, when girlfriend (and hyper-intelligent-sentient-oil-being) Heather returned Bill to her original form, she outfitted her in a distinctive light blue jacket with large lapels and a different top.

So does the fact that Bill is wearing the first jacket and top in this picture mean her next meeting with the Doctor will actually take place prior to all that Cybermen palaver, possibly immediately beforehand?

Well, maybe – except, in the glimpse we see of Bill being reunited with the Doctor in the Christmas special trailer she seems to be wearing the same light blue jacket she had on after being rescued by Heather, which suggests its post-Cyber-Bill, seeing the Doctor for the first time since she left him for dead in the Tardis (her joyful reaction only backs that up).

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So why is Bill wearing her earlier outfit in these publicity shots for the Christmas special? Could it be that we’ll get to see Bill from two different points in time – before and after the whole Cyberman debacle? Or perhaps at some point she simply decides to change clothes. After all, even an alien-oil-being needs a new look once in a while…

2 Bill's badges

Talking of that jacket, what about the two trademark Bill Potts badges stitched on to it? A lightning bolt and a hamburger. We've seen before that Bill's badges can be precursors of what's to come in her adventures with the Doctor – could these be another example of that?

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And if so, what might they signify? Well maybe, just maybe, the burger is a sly reference to a certain American-diner-style Tardis, as piloted by one Clara Oswald? Rumours have abounded that Jenna Coleman will be making a cameo in the episode and it seems only fitting that the Twelfth Doctor's first and longest-serving companion should pop back to say goodbye as Peter Capaldi bids a final farewell (just like Amy Pond did for Eleven in another story penned by departing showrunner Steven Moffat). Could this innocent looking burger be confirmation of that?

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And if Clara is returning, might she also be accompanied by her Tardis co-pilot Ashildr/Me? How does that relate to a lightning bolt, you ask? Well I’m grasping at straws here but we first met Ashildr during a battle with an alien pretending to be Odin, father of Thor the thunder god. No? Er, how about… the Doctor used electric eels to defeat Odin and his Mire warriors, and lightning = electricity… Er… Hmmm.

3 Bill’s sparkly boots

Ok, when I started this I admit I hadn’t intended quite so much of it to be about Bill's fashion choices – but it's hard not to mention those sparkly boots.

Mostly because they are such a strong look but also because they're kind of… glassy and the new episode synopsis that comes with this picture reveals that the Doctor and co will be facing “enchanted glass people”. Maybe this Bill is an enchanted glass person, hence the other Bill in the other jacket? No? I’ll get my coat. The one with the badges on it…

4, 5 The Doctor's battle-scarred coat

We know the Doctor finds himself on a First World War battlefield in the Christmas special so you might wonder if those holes in his coat have been made by shrapnel, or even bullets, but cast your mind back to the end of the last series and you’ll recall that his outfit was already looking pretty battle scarred after getting on the wrong end of a scorching blast from a Mondasian Cyberman. I’m pretty sure that also accounts for the shredded cuffs and coattails. It seems that, unlike Bill, the Doctor hasn’t had time for a costume change…

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6 The light fantastic

What is that coruscating light the two Doctors and Bill have their eyes fixed on? It’s impossible to say exactly, but what’s the betting it’s got something to do with those “enchanted glass people” mentioned in the synopsis and their habit of freezing moments in time?

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7 The regeneration game

Talking of shining lights, that golden glow emanating from the Twelfth Doctor’s hand is a reminder – as if we needed it – that he’s on the brink of regenerating during this episode. I wonder what the Thirteenth Doctor is going to think when she finds herself wearing those battered old clothes…

Doctor Who: Twice Upon a Time will air on BBC1 this Christmas