During World War I, the 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, in reality, is 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.