Digital Spy was lucky enough to attend a preview screening of the hour-long festive instalment earlier this month and, while we're sworn to secrecy, we can tell you that the nature of what it means to be human is also a key theme. By episode's end, even The Doctor himself has come to resemble his favourite species just that little bit more...
And as for the tone? In short, it's Christmas - don't expect scares or timey-wimey complications. Steven Moffat has pulled back on his usual flourishes, delivering what is actually a rather straightforward adventure. 'The Doctor, The Widow and The Wardrobe' is simple, light-hearted fun - think more 'Runaway Bride' than 'The Wedding of River Song'.
Much has been made of Outnumbered star Claire Skinner's appearance in this special, and while her character Madge Arwell is absolutely central to the plot - with Skinner's name following Matt Smith's in the opening credits - it's really Holly Earl, as Madge's daughter Lily Arwell, who assumes the role of fill-in companion.
The 19-year-old is terrific, giving a spirited performance as the inquisitive Lily. The special's supporting cast is pretty much solid all round, though it's a pity that Bill Bailey and Arabella Weir - as the bungling Dorxil and Billis - feature only briefly and share no scenes with Matt Smith's Time Lord.
Another big name in the episode's cast is, of course, Alexander Armstrong, playing the small but pivotal role of Madge's husband Reg Arwell. The actor, comedian and television host told Digital Spy that he was thrilled to have landed a part in 'The Doctor, The Widow and The Wardrobe'.
"I'm acting with Claire Skinner in a little World War II setting - it's a very sweet Christmas story," Armstrong explained. "Very nice, very touching, very stirring - very exciting indeed!"
Praising showrunner Steven Moffat, he added: "I'm really pleased to have got in, particularly while Steven's in his pomp. It's a sort of 'purple patch' of Doctor Who and it's lovely to be right in there!"
Armstrong, who voiced super-computer Mr Smith in Who spinoff The Sarah Jane Adventures from 2007 until the show's end earlier this year, admitted that he is thrilled to be making an on-screen appearance.
"They invited me to come and be Mr Smith personified [on Sarah Jane]," he revealed. "There was an episode [planned] where he steps out [of the computer]. They were ready to write that up and make it into quite a fun role, but I just wasn't available.
"So they've always had me on their radar as someone they wanted to get in. This [Christmas special] was a lovely, lovely couple of weeks I spent in Cardiff - really very good fun."
Doctor Who, 'The Doctor, The Widow and The Wardrobe', airs on Christmas Day at 7pm on BBC One.