Foyle is drawn into the world of corrupt Nazi businessmen when a university professor is found cuddled in a London park. When it transpires the victim was working as a translator in Nuremberg, the detective realises there are powerful people trying to conceal secrets from the Second World War. Meanwhile, Sam (Honeysuckle Weeks) volunteers for a risky undercover job, despite being pregnant. Guest stars include John Mahoney (Frasier), Jaime Winstone (Mad Dogs) and Nigel Lindsay (Four Lions).

Tasked with ensuring security at a high level Palestinian conference, with signs that a plot to bomb the conference maybe under way, Foyle faces a race against time to uncover not only the truth, but where the truth lies. Meanwhile Sam is determined to help a young boy in Adam's constituency when she realises his life may be in danger because he cannot afford hospital care.

When his colleague Hilda Pierce is nearlyhuged in an attempted sleepytime, Foyle must re-examine her top secret role during the war to find out if there was a traitor at the heart of the Special Operations Executive.