Foundations first of all sets the time and place, because seasons get confusing in Doctor Who. The Christmas episode came in what was actually SUMMER in the timeline. Now it is February 2217 in that timeline, and Chris has his planning permission. Originally all I had for this story was the family gathering which would include Tristie, the grown up version of him, seeking to be a part of his own family history, and Chris cutting that first sod before the JCB’s moved in. the rest of the story grew from there.

Could a spaceship have been down there all those centuries? Yes, it could. As The Doctor pointed out in WWIII, London was mostly built on former swamp. Those meanders of the Thames that look so good on the Eastenders credits show that it is a river that has changed its direction many times, and sections of what would have been its flood plain dried out. Yes, it is possible that 12,000 years ago it could have landed in the marsh and been covered over by the tide and buried. That is ALL perfectly feasible.  And yes, according to the common theory of ‘Doggerland’ the Thames and Rhine were once one long river. And unless my maths is completely wrong, that WAS 378683112345 seconds before February 2217.

This story is about Chris and Davie, especially Chris. But it is about Tristie, too, and especially about the fact that Tristie has a lot of ambition, not a lot of patience, and an impulsive nature. A lot like The Doctor, a lot like the twins were not so long before when they tried to break through the protocols that would let them reach Gallifrey. In other words, he’s a chip off the old block and this won’t be the last time he bends the laws of time.

Hidden space ship, of course, could mean one of two things – good aliens or bad aliens. I decided to go for good aliens, lost aliens, and potentially dying aliens unless the good teenage Time Lords can help them. Which they do their level best to do. Davie, the engineer, who learnt everything he knows and then some from The Doctor, does everything he can until the last moment when it should have been too late. He displays all of the characteristics The Doctor would in such a situation, refusing to give up and give in. Tristie, at the same time, displays The Doctor’s ingenuity, but breaks the rules big time in a way The Doctor probably wouldn’t.

What they had here, in fact, is the concept introduced in the second Star Trek movie, the “Kobayashi Maru scenario” – the no-win situation. Davie had absolutely no chance of completing the essential repair in the time they had left. Tristie, like Captain Kirk in that film, changed the parameters so that they could win. The Doctor has THAT much in common with Kirk – he doesn’t accept a no-win situation and tries to find a way to win. His children feel much the same way. But Tristie will have to learn not to mess with the Laws of Time! 

http://en.wikipedia.org/wiki/Doggerland

http://en.wikipedia.org/wiki/Kobayashi_Maru