The year is 1981. Tehran is in violent turmoil in the wake of the Iranian Revolution. The Soviets are planning to overthrow the Ayatollah's fledgling Islamist regime. If they do so, one response from America - unknown to the public - would be to use nuclear weapons. This is the story of how at the height of the Cold War, one mysterious double agent, known to MI6 as 'Redwood', revealed the Kremlin's secret plot and prevented Armageddon.

This unsung, hitherto unknown hero of the Cold War, a six-foot-four Russian intelligence officer had a problem, a sexual secret, one that if revealed, would turn his life upside-down. So he reached out to MI6, believing it to have the only solution - in return for the KGB's deepest secrets. And then, facing exposure, he demanded that the British try to smuggle him out of Iran in a high-stakes escape plan.

This is the gripping tale of one man's courage; about friendship, marriage, betrayal and sexual dysfunction; and about how decisions made in secret can have huge, long-term ramifications.

Drawing on never-before-seen material from archives in multiple countries, and interviews with officers from MI6 and MI5, the KGB and CIA, Redwood lifts the lid on how espionage really works, and on an unknown and highly significant Cold War victory. For without Redwood, our world would be very different - and might not exist at all