In the book, the aliens adopt a range of human forms, only one of which was really kept for the screen, the little girl with the balloon. The balloon is a weapon in the original, and was for some drafts of the TV version, but the mechanics of trying to make a balloon deadly in visual terms defeated us. It’s one of those things you can do in prose which might just look silly on the small screen.

Similarly, it’s sometimes a question of putting down solid markers to let viewers know where they are immediately. It’s 1913, not early 1914, to say it’s before the war happens. It’s Mr. Smith rather than Dr. Smith so that nobody calls Smith ‘Doctor’. Mind you, Smith is from Nottingham rather than Aberdeen because David wanted to keep an English accent. And Smith’s parents, originally Sarah Jane and Harry, became Verity and Sidney (after the original series’ creators) when SFX magazine journalist Nick Setchfield mentioned to Verity Lambert, during her interview with Russell, that a character in the book was named after her.

The very ending is interesting. David plays ‘run’ like he’s toying with the aliens, happy to be the Doctor again, when in the book it’s a dark sign that the tragedy has been played out. But that gives a nice contrast with the havoc that comes immediately afterwards. In the book, the Doctor having his finger back is the sign that he’s his Time Lord self again, while in the TV version it’s the return of the glasses (very Clark Kent!) that does the job.

I’m very pleased that the coda, at the war memorial, is as in the book. It’s my favourite bit.

I’m also very pleased that, through accident or design, a lot of the recurring images of my work appear in the TV version. Owls can be heard in the distance, and were first indicated in Russell’s polish of the script. (There’s also a lovely brush with an owl design on it in Smith’s study, though you don’t see it.) So the owls of the book, Rassilon’s messengers who watch over the Doctor, are there in spirit. There’s a female vicar, as there seems to be in almost everything I write. ‘Baxter’ is someone Russell drops into dialogue all the time, but ‘Saul’, also one of his additions, reminds me of Saul the sentient church from my other Who novel, Revelation.

And you see what Smith is eating, in that scene where we’re cutting from his speeded-up list of ‘things not to let me do’? That’s a pear. One of those instructions, in the book, and in the slowed-down version of what you see, is not to let him eat that particular fruit. Because he doesn’t like the taste.