1940. The train is under attack from German fighters. In the darkness, sheltering in a railway tunnel, the stranger in the carriage with Barney and his mother tells them a story to pass the time. And what a story. The story of a young man, a young soldier in the trenches of World War I who, on the spur of the moment, had done what be thought was the right thing. It turned out to have been the worst mistake he could ever have made - a mistake he must put right before it is too late...