In Northern Poland in 1940, at the Nazi war camp Stalag XX-A, two men struck up an unlikely friendship that was to lead to one of the most daring and remarkable wartime escape stories ever told. Antony Coulthard was the privately educated son of wealthy parents and he had a first-class honours degree in modern languages from Oxford. Fred Foster was the son of a bricklayer from Nottinghamshire - he had left school with no qualifications aged 14.

This seemingly mismatched young pair bonded in the prison camp, and hatched a plan to disguise themselves as advertising executives working for Siemens. They would simply walk out of the camp, board a train - and head straight into the heart of Nazi Germany. Which is precisely what they did. Their route into Germany was one that no one would think to search for escaped PoWs. This breathtakingly audacious plan involved 18 months of undercover work, including Antony (nicknamed 'The Professor' by fellow inmates) spending 3 hours every evening teaching Fred to speak German.

They set off for the Swiss border via Germany, doing some sightseeing along the way in Munich and Berlin, taking notes of strategic interest while eating in restaurants and drinking beer with Nazi officers, just yards from Hitler's HQ. But could they make it out alive?