Phil Kelly, a veteran of the Spanish-American War, serves as an American spy during World War I unknown to his mother, fiancée Rose Lockely and friends, who sadly question his loyalty when he fails to enlist. German agents Karl Shamme and John Harris invite Phil to a secret meeting, where he learns of German plans to sink several Allied transports. Phil saves the transports and then is sent to Germany posing as a German aviator. After flying over American lines to warn the Allies of an impending large-scale German offensive, Phil is discovered by Shamme and sentenced to death. Shortly before he is to be shot, Americans bombard the area where he is imprisoned. Although injured in the battle, he is rescued and nursed back to health by Rose.