During World War I, beautiful and patriotic Leslie Selden is courted by two ardent admirers: Jack Wynn, a young man not yet taken by the draft, and Dr. Wolff, a Danish scientist who is actually a German agent. When Jack learns that Wolff is masterminding a plot to bomb several munitions factories and destroy the water system in New York City, he goes to the spy's home and confronts him. Wolff locks him up, then forges a note to Leslie claiming that the young man has run away to escape the draft. Her suspicions aroused, Leslie alerts the authorities and plants a dictograph in Wolff's house, through which she learns of the scheduled bombings. Accompanied by the police, she arrives at Wolff's residence just in time to prevent Jack's murder and the destruction of the city.