Eileen Wells is receiving a call from her fiancé, Lieutenant Masters, when her father, General Wells, and her brother, Gordon, who is a Lieutenant, arrive bringing the startling news that war has been declared against their country by the Government of Lieutenant Masters, who is the military attaché to the embassy of the hostile country. General Wells dismisses him from his house as he is now an enemy. Upon departing for his country Lieutenant Masters returns to bid farewell to Eileen, and she gives him a carrier pigeon so that he may communicate with her. Before leaving for the scene of action, the General and Gordon acquiesce to Eileen's desire to serve as a red-cross nurse. An orderly brings to General Wells' headquarters the announcement that the Prince will, at two o'clock the next day, present the colors to the 5th Battery. This Battery is under command of Lieutenant Powell, who, acting as a tool for the enemy, steals over to the opposing forces to acquaint their commander with the presentation of the colors, and advise a surprise attack at that hour. The traitor quickly returns to his camp. In his own tent, he constructs a bomb, and places the deadly missile in a huge long-range cannon, timing the explosion for the hour of the Prince's presence. Perceiving that there is a traitor in General Wells' army, and realizing the grave danger that threatens his sweetheart's father, after a few moments deliberation, his love for Eileen prevails over his duty to his country. Lieutenant Masters dispatches a note with the pigeon, advising her that a traitor has given information of the color presentation, and that a sudden attack will take place at that hour. Eileen frantically speeds to the front in a motor car, and miraculously eluding the fusillade of the picket, she reaches her brother's camp, and imparts to him the plot. Like a flash he mounts his horse, and rides to the General's headquarters, arriving in the nick of time to save the Prince, his father and staff from the deadly explosion of the bomb. Forthwith a terrible battle ensues, the enemy manifesting splendid heroism, unheeding the multitude of shrieking, bursting shells which mow down many of their number, fairly covering the battlefield with dead and wounded. Gradually all the trenches fall into the hands of the advancing army, save the last one, which, under the command of Lieutenant Masters, offers a most obstinate resistance. The battalion of Lieutenant Wells soon overpowers it; a violent bayonet charge follows, during which Lieutenant Wells witnesses Lieutenant Masters' fall. The enemy is repulsed from its position by Lieutenant Wells' forces, and completely routed. During the interim, Eileen is nobly caring for the wounded soldiers in a field hospital, where her brother finds her, and tells her how he saw Lieutenant Masters fall, firmly clasping his country's flag. Eileen, anxious to learn her sweetheart's fate, induces Gordon to accompany her to the battlefield. After searching for some time, they finally come across Lieutenant Masters lying among the dead, seriously wounded. They have him placed upon a stretcher, and send him to their home, which had been converted into an emergency hospital. Determined to drive the enemy from their last stronghold, Lieutenant Wells volunteers to blow up this fortress. Up and down snow-covered mountains, through the intricacies of barbed-wire entanglements, and overcoming numerous obstacles, he at last reaches the fortress. The sentries guarding the entrance are killed by a bursting shell, whereupon the Lieutenant, entering the court, comes face to face with Powell, who offers his sword to Wells that he may kill him. The latter rejecting the sword, ignites a bomb, the explosion of which shatters the powder magazine, killing and burying under the debris the traitor. Accompanied by strains of martial music, the victorious army marches into the fortress, and receives the surrender of the holding forces, thus consummating a complete victory. Soon after, General Wells has returned to his home, the Prince comes to confer decorations upon him and his son for their heroism. Lieutenant Masters, now convalescing, under the care of Eileen, obtains the consent of her father to their marriage, and receives the praises of the Prince for his services to the country.