Writer: Steven Moffat (well the Doctor Who showrunner and head writer was hardly going to give this gig to someone else, was he?)
Director: Saul Metzstein, who worked on series-seven episodes Dinosaurs on a Spaceship and A Town Called Mercy.
Cast and characters:
Jenna-Louise Coleman will return to take over from Karen Gillan (and Arthur Darvill) as the Doctor's new companion following her unexpected and puzzling appearance in series seven opener Asylum of the Daleks. She was known in that episode as Oswin Oswald, but we're led to believe her character will be called Clara Oswin.
Neve McIntosh and Catrin Stewart are also back as Silurian Madame Vastra and her human "companion" Jenny (hint: they're more than just friends), both of whom were last seen in series-six episode A God Man Goes to War, joining the Doctor in his assault on Demon's Run.
Having previously played the Time Lord's ninth incarnation in digital animated adventure Scream of the Shalka (as well as briefly appearing as an unofficial Tenth Doctor in a 1996 Comic Relief sketch), Richard E Grant is our Christmas baddie, along with Tom Ward (who Silent Witness fans will know as Harry Cunningham in the BBC pathology drama series).
Plot, setting and questions:
It's a Victorian-set episode, as confirmed by the teaser trailer – which shows Coleman crinolined and bonneted and Grant in a top-hat – not to mention numerous leaked on-location shots. Whether it actually takes place at Christmas remains to be seen (but cross your fingers for snow!).
Could this episode end with Vastra and Jenny travelling with the Doctor? We know one of Mark Gatiss's upcoming episodes will star Diana Rigg and Rachel Stirling and photos from the set have shown those two filming with Matt Smith, Coleman, Mackintosh and Stewart, all still in period garb...
How does the Asylum of the Daleks Oswin (who had been converted into a Dalek) relate to the companion Oswin? Will we see the Doctor saving her from her apparent fate? Are different timelines involved, or what...?