When Harold Fry nips out one morning to post a letter, leaving his wife hoovering upstairs, he has no idea that he is about to walk from one end of the country to the other.

He has no hiking boots or map, let alone a compass, waterproof or mobile phone. All he knows is that he must keep walking. To save someone else's life.

Harold Fry is the most ordinary of men. He just might be a hero for us all.