Still reliving the past, it’s the year 1915 and Inspector Blair is serving as a special investigator during the war in France. The sounds of battle rage in the distance when a case of a spy is brought to Blair. Lieutenant Ralston is an interpreter assigned to Blair to tour the trenches, and gather intelligence. Has someone been signalling the enemy?
There’s a suspicious bomb crater, but Blair hasn’t spotted any odd behavior to indicate any spies or signalling. Ralston however, reports that he saw a signal light, and the source was actually in back of the troops, where nobody was watching. The next night, Ralston shows Blair the strange light. A man is picked up, and taken in for questioning. Ralston seems to be the man of the hour, but as Blair is about to relinquish his duties he springs a surprise and accuses Ralston of being the spy. Blair reveals the trick that Ralston used to send the signals from remote control. In epilog, Blair is unsettled as he recounts the events that followed the arrest, and the military firing squad. Despite being a spy, Blair admires and respects Ralston’s bravery in facing his doom.