The train is under attacks 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 he thought was the right thing. It turned out to have been the worst mistake he ever could have made - a mistake he must put right before it is too late.