Jack Duncan returns from the war in France to his wife and baby and learns that his job as a draftsman at the Loring Steel Mills has been taken. Given work in the machine shop, Jack becomes the prey of Red agitators who want him because of his popularity with soldiers. The Reds cause Jack's discharge just when his house payments come due, and when they convince him of the injustice of his situation, he joins their ranks. After learning of plans to burn the factory and Loring's home, and start a riot in the town, Jack is won over by a socialist's arguments advocating mild reforms. At a meeting of workingmen, Jack praises Americanism. He warns Loring and, with soldiers at a nearby camp, quells the riot. After a woman agitator kills her comrades and then shoots herself, Jack arrives home to save his wife from an attack by a Red ringleader. Jack is then made a foreman at the mill.

In a Virginia resort town in August 1918, Christopher Brent is viewed as a slacker because he refuses to enlist. Secretly, Christopher is observing German spies who are passing information about coastal fortifications for invasion preparations. Seeing Christopher consort with Mrs. Miriam Lee, also from the secret service, his fiancee Molly Preston, who had been bothered by the talk about him, becomes jealous. When Molly's brother Norman discovers a German code book in Mrs. Lee's possession, Christopher, who obtained the book when he destroyed the wireless of the chief spy, Carl Sanderson, who also loves Molly, is suspected of aiding the Germans.