The Homecomers went through a couple of different formats before I settled on the storyline I eventually went with. In one, the original abductees were at the bottom of the reservoir in their original bus, having been there all the time while the aliens stole their identities. A picture on Wikipedia of the Craigmaddie reservoir drained for repairs and looking distinctly sinister gave me the idea. It would have made for a much darker and nastier ending than the one I have heer, and I have considered writing that version as an alternative for any reader who thinks that Torchwood shouldn’t have too many happy endings.
Anyway, I may still have plans for Craigmaddie reservoir to harbour an alien secret, yet. Watch this space. Meanwhile Bardowie Castle was a nice little find when I was looking for bodies of water north of Glasgow. It has enough sprawling outbuildings to be a perfect location for this story which needed to be set outside the Hub. It is apparently in private ownership now. But that could well be a cover for U.N.I.T. or any other secret organisation.
Since I had decided to make the Homecomers innocent victims after all, there had to be something controlling them. That needed a bit of thinking about, but there are only a certain number of ways people are controlled in science fiction. An obvious one is implants in the head. A less obvious variation is organic implants. It HAS been done before quite effectively in Star Trek: Wrath of Khan, when larva wrapped around the cerebral cortex made victims open to manipulation and control.
The method of killing the bugs in the heads of the Homecomers, by reversing their signal, is a little closer to home. It is a simpler form of what happened in the final resolution of Torchwood: Children of Earth, except nobody had to die. This wasn’t exactly an attempt to copy the CofE method of dealing with aliens. But it may appear that way to some people, perhaps.