While getting into his car on the evening of February 16, 1978, the chief of the CIA"s Moscow station was handed an envelope by an unknown Russian. Its contents stunned the Americans: details of top-secret Soviet research and development in military technology that was totally unknown to the United States. From 1979 to 1985, Adolf Tolkachev, an engineer at a military research center, cracked open the secret Soviet military research establishment, using his access to hand over tens of thousands of pages of material about the latest advances in aviation technology, alerting the Americans to possible developments years in the future. He was one of the most productive and valuable spies ever to work for the United States in the four decades of global confrontation with the Soviet Union. Tolkachev took enormous personal risks, but so did his CIA handlers. Moscow station was a dangerous posting to the KGB"s backyard. The CIA had long struggled to recruit and run agents in Moscow, and...