Fast Forward was inspired by an episode of one of the Star Trek franchises, I think, possibly, Enterprise, which I caught a very small bit of on Freeview. In the episode, a capsule had been found, containing a body, and crew members were infected with rapid aging from it. All was right in the end, of course.

I tied this idea in with an idea I had toyed with ever since I wrote Son of The Master, the story in which The Doctor had to become the Human, John Smith. In that story, John Smith does sleep with Rose. It is implicitly suggested that they had sex. And I then had the thought – what if Rose got pregnant again by the Human version of The Doctor. But I didn’t really want a series of stories with Rose pregnant again. This rapid aging idea gave me the opportunity to have the Human baby story resolved in one story.

The victim being a Chula warrior, of course, takes us all the way back to 2005, the wonderful Christopher Eccleston, 9th Doctor series, and the episodes, Empty Child and The Doctor Dances, in which we first met Captain Jack and were introduced to the concept of nanogenes that repair damaged people, but sometimes get it wrong. The idea of a Chula warrior delivering a dirty bomb containing bad nanogenes to kill their enemy through this rapid aging followed from there. And the analogy with the dropping of the atom bombs on Hiroshima and Nagasaki and The Doctor’s own terrible part in the Time War were inevitable.

Of course, The Doctor would work it out. But I wanted the new baby to reach the age of about five months before that happened. This would make her roughly the same age as the premature twins by the time the aging was stabilised and they got back to Earth. That way, in future reference, the three babies would be referred to as the triplets, possibly.

Of course, this is also an example of a story which mainly takes place on board the TARDIS. I think there ought to be more stories set within the limitations of the TARDIS. As early as 1964, it was proved a winning formula with the two part classic Edge of Destruction. Finding ways of using the TARDIS for stories is a challenge I like to rise to from time to time.