Each Christmas special plays with it's Christmassiness in different ways. Killer Santas, Christmas trees, baubles; a Victorian Christmas; riffs on traditional Christmas tales. Last Christmas takes Christmas's biggest icon - only tangentially involved in two previous specials, and puts him centre stage - along with elves, reindeer and a sleigh. But this is really where the Christmas element begins and ends. The rest of the episode is one of Doctor Who's scariest episodes set on an isolated base with creatures that kill you while you sleep, hugging your face in the process. Only Doctor Who could mash up Father Christmas, A Nightmare on Elm Street and Alien and serve it up as Christmas family entertainment!

It's a stonking episode. Capaldi is on fire. I've never been shy about my dislike for the way the 12th Doctor was characterised, particularly in Series 8 which directly preceded this special, but in Last Christmas he's much more to my taste. His spikiness is still there, but so is the fun, the silliness, the desperate concern for his companion and all the Doctory traits that seemed to get lost somewhere in his regeneration from 11 to 12. His unravelling of the mystery as he pieces the clues together is wonderful stuff. Jenna Coleman, too, does great work as Clara. In a way, it's a shame she decided not to make this her last story because it would have been a real high to go out on (and we'd have been spared all that nonsense at the end of Series 9). The dreamscape she finds herself in with Danny is desperately sad and hopeful at the same time and it feels almost cruel when the Doctor eventually breaks into her dream to save her, even though we know he has to do it. (Samuel Anderson is also great in this brief reappearance)

The guest cast all provide excellent support, especially would-have-been companion Shona. It's also a delight to finally see David Troughton appear in an episode, as well as Dan Starkey finally getting his actual face on screen (along with Misfits' Nathan McMullen as a couple of hilarious elves). But of course, it's Nick Frost as Santa who steals the show somewhat. He's the right balance of reassuring and unsettling meaning the viewer is never quite sure if he's supposed to be real or not. Even when he is revealed to be a product of the dream, he still feels like a real person.

The Dream Crabs are a horrific addition to the world of Doctor Who monsters. The way they make their human victims into monsters themselves is clever and, although they pay an undisguised debt to Alien's facehuggers, their scuttling and leaping is quite terrifying. The concept of dreams within dreams is also unsettling and adds to their chilling modus operandi.

There are some lovely scenes where the scientific crew wake from their group dream, although I feel Moffat missed a trick by having them all wake up in contemporary times - particularly as the script flags up the fact they could all be from completely different times and places. Maureen Beattie waking in a wheelchair is quite sad though. The one part of the ending I don't feel works as well, and this maybe because of the decision for Clara to carry on as the Doctor's companion, is Clara as an old woman. It's possibly one dreamscape too far and I think it's too obviously a dreamscape for it to have much impact on the viewer.

It's a minor gripe though in a story which, for me, re-establishes the Doctor in his 12th incarnation, gives us a great could-have-been companion, a scary monster, some great comedy and a lot of thrills and spills.

Yeah, it's fine? As will become tradition with Capaldi Christmas specials, it has a fantastic final few scenes - in this case, the sleigh ride and the Doctor talking with elderly Clara - but the episode beforehand takes a little too long to properly get going and then keeps repeating itself; and not really in a creative way. It's just replaying the same beats it had presented before.

Santa's there... just because? Ah well, it's only just a dream. OR IS IT? Also the inclusion of Danny Pink is a really nice coda for Clara's story in S8.