In the shadow of the Cold War a letter from Oleg Penkovsky (Merab Ninidze), an agent of the Soviet Union, is received by MI6 stating the concern of Penkovsky about world safety and his anxiety about a nuclear war. So Emily Donovan (Rachel Brosnahan), a CIA agent, reached out to MI6 agent Dickie Franks (Angus Wright), who recruited British salesman Greville Wynne (Benedict Cumberbatch) to be their spy.