The astonishing true story of how the CIA, MI6 and a Soviet defector saved the world in 1962, as told in the new film, The Courier, starring Benedict Cumberbatch.

In August 1960, a Soviet colonel called Oleg Penkovsky tried to make contact with the West. His first attempt was to approach two young American students in Moscow. He handed them a bulky envelope and pleaded with them to deliver it to the American embassy.

MI6 and the CIA came to believe Penkovsky was genuine and so the two agencies decided to run the operation jointly. It ran right through the Berlin crisis - in an astonishing near-miss, Penkovsky learned that the Wall was going to be built four days before it happened but was unable to contact his handlers - and the Cuban Missile Crisis, in which rocket manuals Penkovsky had handed over were crucial in determining what President Khrushchev was doing, and helped President John F. Kennedy and his team end the crisis and avert a nuclear war. Penkovsky, codenamed HERO, is widely seen as the most important spy of the Cold War, and the CIA-MI6 joint operation to run him has never been bettered.

But had the KGB already 'turned' Penkovsky and were the Russians making sure he saw the information they wanted him to see? If so, it may even have been possible that the whole Cuban Missile Crisis might have been a Russian deception operation.

Thrilling, evocative and hugely controversial, Dead Drop blows apart some of the myths about one of the Cold War's most well-known operations as the world stood on the brink of nuclear destruction.