I've just written the dramatic climax, which includes lots of derring-do and the Doctor being heroic. (Finally.) All that's left to write is a short epilogue. It's going to clock in around 55,000 words.
It was inspired by the simplest of exchanges in a Big Finish Doctor Who audio, 1001 Nights:
Nyssa: You’re quite sure this outfit isn’t a little too showy? Oh.
Doctor: Nothing’s too showy for the Grand Coronation of the High Hierophant of the Five Revealed Truths. Oh.
N: We’re not at the Celestial Basilica, are we?
D: Apparently not.
N: Then where are we?
D: I’m not sure. Remote outpost, maybe? Or some kind of fortress? Not exactly bustling with life.
N: It’s a prison, isn’t it.
D: I admit the fifty-foot-high wall does tend to give that impression.
N: I had enough of prisons on Folly. Can we go?
<Cries for help>
D: Did you hear that?
N: Doctor. The Coronation of the High Hierophant, remember? Perfumed rain, falling from clouds sewn with powdered diamonds… you wouldn’t want to miss that.
D: I’ve had the invitation for the past 300 years, Nyssa. I can wait a little longer… come on!
( Babbling about how the story came together... )