In the midst of this is a 1914 World War I battlefield, where Mark Gatiss’ British soldier (and Gatiss is brilliant) is pointing a gun at Toby Whithouse’s wounded German troop. A stand-off, and not a happy one. That much has been revealed in photos from the episode. Everything else story-wise, I’m steering clear of for this spoiler-free preview. Anybody who even thinks of spoiling an episode like this deserves a very, very hard stare.

Instead, let me report that so, so much of Twice Upon A Time works. I found it a wonderful wallop of an episode, with strong emotional moments, an ensemble of characters where I cared and was engaged with every one. And, at the heart of it, the bickering between two Doctors, both in different ways exasperated with each other. David Bradley is clearly having an absolutely ball recreating William Hartnell’s first Doctor, a man confused with the state of what’s going on around him, and not afraid to voice it. Capaldi’s Doctor, meanwhile, is hardly in the best of shape, correcting his earlier self but also having his fair share of fun. There’s a lot of laughs between the two of them, in the midst of an episode with an otherwise slightly more sombre feel.

Capaldi’s performance? Well, what do you think. From the moment he stepped into the world of Doctor Who, it felt like he owned the role. For his finale, his work is sublime. Generous, haunting, funny and utterly moving, his farewell is brilliant. Again, I’ll leave the detail there for now. We’re sure going to miss him, though.

It’s premium Steven Moffat writing we get here, too, and finds him ending on a very high point as well. Moffat’s script gives him slightly fewer balls to juggle than he occasionally has tasked himself with, and it really pays dividends. The pacing of Twice Upon A Time is terrific. There’s no rush to suddenly wrap things up, there’s no skimping over the Doctor Who story at the heart of the episode (and there very much is one), and there’s time built in for some often really quite profound conversations. There are surprising moments that hit really hard, because they’ve been given the space to.

A word, too, for the sheer look of Twice Upon A Time. The preview we saw was projected onto an IMAX screen, and it looked at home there too. The lighting work isn’t often singled out in Doctor Who write-ups, but it really should be here. There’s a flavour of one or two classic movies, and a real sense of scale to some of the bigger moments. One of Moffat’s finest decisions on Doctor Who has been to get director Rachel Talalay involved, and her direction is really something. Here’s hoping Chris Chibnall hires her back.