Based on the 1956 book by Kendal Burt and James Leasor, The One That Got Away chronicles the true story of Oberleutnant Franz von Werra.

An interesting site on "Aces of the Luftwaffe" provides some details:

Von Werra was captured and imprisoned in England. He twice attempted to escape...but was recaptured both times. After his second failed escape attempt, von Werra was sent to a prison camp in Canada. He managed to escape...and made his way through the USA, Mexico, South America and Spain to reach Germany...Von Werra was the only German prisoner of war held by the British to successfully escape and return to his homeland.

(The US was neutral at the time.)