Ben MacIntyre on The Spy and the Traitor, in conversation with Kai Bird.

grew to see his nation's communism as both criminal and philistine. He took his first posting for Russian intelligence in 1968 and eventually became the Soviet Union's top man in London, but from 1973 on he was secretly working for MI6. For nearly a decade, as the Cold War reached its twilight, Gordievsky helped the West turn the tables on the KGB, exposing Russian spies and helping to foil countless intelligence plots, as the Soviet leadership grew increasingly paranoid at the United States's nuclear first-strike capabilities and brought the world closer to the brink of war. Desperate to keep the circle of trust close, MI6 never revealed Gordievsky's name to its counterparts in the CIA, which in turn grew obsessed with figuring out the identity of Britain's obviously top-level source. Their obsession ultimately doomed Gordievsky: the CIA officer assigned to identify him was none other than Aldrich Ames, the man who would become infamous for secretly spying for the Soviets.