Yvonne von Krutz, a Belgian, lives with her German husband Karl, whom she was forced to marry, and her spirited little brother Jacques in a farmhouse on the Belgian countryside. With the German invasion of Belgium, Karl joins the German forces, and Jacques is taken to a reformatory to be trained as a munitions worker. When Karl is taken prisoner, Capt. Jefferson Strong, an American engineer, assumes the German's identity and discovers an underground supply of explosives near the von Krutz farm. By means of a tunnel, the Americans plan to mine the explosives. To save Jacques and a group of children from the munitions factory, however, Jefferson sends them across the American lines through the tunnel, but they lose their way, and he is forced to disable the mine. Jefferson is court-martialed, but King Albert of Belgium, who has befriended little Jacques, intercedes on his behalf. Learning that Karl has been killed, Jefferson pursues his budding romance with Yvonne.