August 1940 and Foyle solves murders, an art theft, a suicide, and tracks down his son who is imprisoned because he is suspected of spying, when assigned to a secret unit developing and testing improved Radar systems.
A pretty good episode of this excellent series. A good supporting cast including Anton Lesser, Roger Allam, and Stephen Moore. ( BTW if you are wondering why Stephen Moore's voice might seem so familiar, he was in the Hitch Hiker's Guide to the Galaxy.)
If you are a WWII buff you will undoubtedly spot various historical inaccuracies, but for the average viewer these won't be apparent. However I did notice that the Spitfire seen in most of the scenes didn't seem quite right for the era; it is actually a Mk IX that saw service in 1943, with cannons, a more powerful Merlin engine in a longer nose, with extra radiators and a two-stage supercharger etc. , none of which were current in august 1940.
Lots of strands to this plot but overall a very enjoyable episode.