Things get very difficult and dangerous too, when their pet collie, Billy, gets into serious trouble. Somehow the children have to find a way to save the dog. However, they have to outwit a gang of criminals to get the proof they need. Help comes from two unexpected sources, one an Italian prisoner of war and the other a sergeant in a commando regiment which is based near to the farm. Can they find what they need, in time to save the dog?