We’re just over 24 hours away from the penultimate episode of Doctor Who Series 9, Heaven Sent, and show-runner and writer, Steven Moffat has given us a hint at how this story came about.

As you’ve no doubt heard, it’s a single hander – the first in the show’s history – with just Twelfth Doctor, Peter Capaldi, and Jamie Reid-Quarrel as the Veil.

Moffat told Radio Times:

“I’m yet to find out whether I’ve just gone mad or not. It occurred to me that I had just written a huge monologue for him at the end of [The Zygon Inversion]. Ten minutes. I was typing forever in that. And I just thought, ‘maybe we don’t need anyone else – we don’t need to cut to anyone nodding – it’s just him?'”

The Zygon Inversion, co-written by Peter Harness (Kill the Moon) and Moffat, featured a stunning scene in which Capaldi plays off Jenna Coleman as Bonnie the Zygon, talking her out of war.

If we’re in for 55 minutes like that, Heaven Sent should be astounding.

The writer further said playing with the format was something they’d be striving to do since it came back in 2005:

“If you’re not going to try things that scare you a bit, that scare everybody a bit, then it’ll feel what it must never feel – it’ll feel like an old show. I remember when Russell T Davies first brought it back, he said, ‘we can’t ever make it feel old. It always must feel like a brand new show.’ And that worked, and we carried on.”

Peter Capaldi also was enthusiastic about the episode likening it to a much-loved Second Doctor classic, The Mind Robber:

“I love things that seem to be 100% undiluted Doctor Who. And that’s what this episode seems to be to me. It is challenging because you realize that if the audience get bored with me that’s really bad news. But there are more colors and angles to it than I’m suggesting…”

Frankly, we can’t wait!

Heaven Sent airs tomorrow at 8:05pm, and will run for an additional ten minutes.