Throughout the Cold War both sides sought intelligence about their opponents using spies, satellites and other means. For political reasons, scientists working on the Manhattan Project provided nuclear secrets to the Soviets. British agents George Blake and Kim Philby passed on to the Soviet Union the identities of Western intelligence assets, and the presence of the Berlin Tunnel. Conversely, Soviet Colonel Oleg Penkovsky gave the West vital details of Soviet nuclear vulnerabilities. Intelligence services are also used to silence dissent, in particular in East Germany. After the Cold War an investigation revealed the Soviet Union had been aware of a number of double agents operating in its midst from information provided by a CIA mole, Aldrich Ames. One such agent, Oleg Gordievsky, managed to flee the Soviet Union, but Adolf Tolkachev and Dmitri Polyakov were arrested, tried and executed. Interviewees include Markus Wolf, Ted Hall, Oleg Kalugin, George Blake, Yuri Modin and Aldrich Ames (who was serving a life sentence). The pre-credits scene shows Polyakov being arrested by the KGB.
