To add to what most of the other commenters have written, this was a complex episode, with several different threads seemingly separate, but came together believably by the end of the episode.
One of the things I find so impressive about Foyle's War is how the writers seem able to keep creating so many sympathetic, yet suspicious secondary characters. We're leery of them in one scene, and in another we're feeling their hurt, and their joy, while never quite letting go of our previous suspicion.
Along with creating three dimensional secondary characters, this episode also managed to incorporate emotional stories for both Detective Foyle and his driver Samantha.
Another intelligently written and heartfelt episode.