This drama is based on the real life events of CIA counter-intelligence officer Sandy Grimes (Jodie Whittaker). The story takes place in 1985 during the end of the Cold War. Sandy and her partner Jeanne Vertefeuille (Harriet Walter) have vowed to find the mole that would turn out to be the most notorious traitor in US History, Aldrich Ames (Paul Rhys). Sandy is in a race against time to save the Soviet intelligence officers from being caught and killed. Also a beautiful wife and mother, Sandy lives her own double life and has vowed to stop at nothing until she uncovers the truth.