At the CIA's Studies in Intelligence web pages, I came across the Cold War story of Adolf Tolkachev, a military aviation electronics expert Over a period of nine years, he provided the CIA with a large amount of highly sensitive information on Soviet avionics, cruise missiles, and other secret technologies. In 1985, Tolkachev was arrested while trying to pass secret materials to the Americans. Tolkachev was executed in 1986 by the Soviets for high treason.
The report gives an inside story on why and how he defected, his motivation, the first contacts with the CIA in Moscow, the Agent communications and many other details. It shows how Tolkachev took ever larger risks, got into trouble, the exfiltration planning, how he was compromised and finally arrested by the Soviets. This story gives a good view on the dangerous life and trade craft of secret agents. The complete story is found at Tolkachev, A Worthy Successor to Penkovsky.