The lives of the four children at Clifftop Farm become very difficult and dangerous when their beloved collie, Billy, gets into serious trouble. The youngsters are compelled to devise a plan to rescue their dog. However, to get the crucial evidence they require, they must outsmart a group of criminals. Unexpected assistance emerges from two surprising quarters: an Italian prisoner of war and a sergeant in a commando regiment stationed near to the farm. In a race against time, will the children succeed in locating the vital information needed to secure the dog's safety?