‘I’m the Doctor, and you’re in the biggest library in the universe. Look me up.’ There are more portents of the coming Moffat years, particularly the idea that the Doctor can make ‘whole armies turn and run away. And he’d just swagger off back to his TARDIS and open the doors with a snap of his fingers’ which is essentially the ending of The Eleventh Hour (‘Basically… run’) and a chunk of The Pandorica Opens. Miss Evangelista’s veil-clad avatar looks like a prototype of Madame Vastra, and River’s ultimate fate – dying, but then living forever – is the one Moffat reserves for most of his female favourites including Clara, Bill and Ashildr. The Vashta Nerada speaking through their victims is essentially the new method of the Weeping Angels in The Time of Angels.

But this isn’t a random selection of ideas Moffat mines in the future. This comes together satisfactorily (although, despite the best efforts of all concerned, with less punch-the-air triumph of The Doctor Dances), as the Vashta Nerada’s presence, CAL’s true identity (very Oswin Oswald) and the nature of Lux’s expedition, and the truth of the Library users’ disappearance all play into each other in a way The Poison Sky’s ending didn’t.

Largely, it achieves this with a sub-plot about Donna’s imaginary existence inside the Library’s data core as she starts a family with Lee, but gradually realises that she’s living inside an elaborate illusion. These scenes are lovely for giving Catherine Tate a very different role than normal – she makes a much more convincing parent than the Doctor to his daughter – and foreshadows the end of the season where she’s once again made to forget by a doctor: ‘The memories are all still there. The Library, the Doctor, me. You’ve just been programmed not to look.’ I wouldn’t lose these for the world, and they show, rather than just telling, what’s happened to the Library’s visitors. But mostly they help to hide that there’s not much going on bar running about for the Doctor and River until they reach their own journey’s end.

But, like dying, two-parters give us size. This is ultimately Moffat’s statement of intent for his version of the show. Naturally, it synthesises the elements that made his earlier episodes successful, and looks forward to his interest in exploring childhood, intricate story arcs, and Doctor who? Half its success its it’s all tease with no resolutions – we don’t know for sure the circumstances when the Doctor would reveal his name or the true nature of his relationship with River. For all that it features River’s death, this is all about beginnings not endings, and the promise of things to come.

Next Time: Midnight