Foyle is assigned to protect an eminent art historian, a former Nazi who is now an important MI5 asset. Sam has some big news for Adam.
Foyle investigates the death of several high-ranking defectors from the U.S.S.R., and uncovers a mole working at an MI5 interrogation centre. Sam tries to help her husband with his by-election campaign.
Foyle returns from the U.S. and is soon approached by MI5, who want to recruit him to investigate a Soviet spy ring operating at the heart of the Establishment. Sam's husband has parliamentary ambitions.