Its code name was "Operation Gold," a CIA plan to construct a clandestine 1500-foot tunnel into East Berlin to tap into critical KGB and Soviet military telecommunication lines. Success would provide access to a vast treasure of intelligence, but exposure might spark a dangerous confrontation with the Soviets. Yet as the Allies were burrowing into the German soil, MI6 agent George Blake, code-named Agent Diamond by his Soviet handlers, was burrowing into the operation itself. Drawing upon archival research, secret documents, and rare interviews with Blake himself, Steve Vogel provides a heart-pounding account of this true Cold War espionage case, and creates a portrait of the most damaging mole of the Cold War.