The new security services takes a dim view of all those people who worked for the Special Operations Executive during the war. A lot of them cannot get job with MI5. It might because they did not go to the right school or have the right connections. Foyle though has use for someone rejected for a job by asking to make a daring attempt to infiltrate an establishment that holds people against their will.
Foyle is still getting used to being a spy rather than a policeman. Still when Russian defectors living in MI5 safe houses get garroted, an ordinary woman disappears and a man collapses in hospital speaking what looks like Russian. Foyle is the man to investigate especially a hospital doctor is later found dead.
The place is Barton Hall, a military establishment which spies on Russian transmissions and decodes them. It is run by Colonel Galt who is not keen on Foyle snooping about.
Meanwhile Sam is campaigning with her husband Adam for the by election. Adam decides to help out a mother whose daughter has gone missing, she has the same name of someone who defected behind the iron curtain.
It always seems too convenient that Sam's home life and professional life always seems to come together. I think once Anthony Horowitz decided to give Sam a husband and have him run for political office he felt that the element of that story should be bought into the main mystery somehow.
There is a lot going on this episode and some misdirection. The doctor's death is an important clue and Foyle also wants to help out the late doctor's wife who was a Jewish refugee who is at risk of being deported now that her husband has died. A leisurely paced story with too many stiffed upper lip characters for my liking. They end up looking like caricatures rather than real people.