Five and Nyssa go to 18th Century France, maybe.

This is definitely the best one of the trilogy, with a cracking first part, tension throughout and some really lovely science fiction concepts and worldbuilding. It's never in your face, but every twist presented seems logical and the conclusion has some real weight behind it, also due to the trilogy guest character.

On the downside, the music was downright weak and apart from the conclusion this was the guest character's weakest performance in the trilogy.