The last-ever episode. When his colleague Hilda Pierce is targeted by an assassin outside MI5, Foyle must re-examine her top-secret role during the war. He suspects the shooting could be connected to the hunt for a traitor within the Special Operations Executive who may have been behind the deaths of nine agents in France. Meanwhile, Sam is faced with a dilemma when Adam and Glenvil crack down on the black market in East Peckham. Guest stars include Conleth Hill .