This is one of the great untold stories of the 20th century.

It is a firsthand account of a mission by an SAS soldier sent behind the Iron Curtain by MI6 to find someone who didn't necessarily want to be found and how, on a follow-up mission, he found himself manoeuvring against a mysterious KGB officer and a murder plot by Kremlin hardliners.

If the plot had succeeded, it would have given the Russians the excuse they were looking for to roll out the tanks across East Germany, the Berlin Wall would not have fallen - and the map of Europe would look very different today.

It tells of rooftop chases, the interrogation of terrorists to gain vital information, a beautiful East German female (who he suspected of being a Stasi spy), betrayal by people he trusted, and an escape through forests pursued by enemy agents and ending in a climactic gun battle at Colditz castle, formerly used by the Soviets as a psychiatric hospital to detain dissidents.

In James Bond novels, it is MI6 operators who carry out this type of work, but in reality, when facing a committed foe in an isolated and deadly environment, the intelligence agencies call upon members of the British Special Forces. This is the first insider account of how UK operators working undercover do what needs to be done in order to protect the UK's interests abroad - revealing their hidden hand in world events.