Ruth Carroll, a schoolteacher in New York's Lower East Side, meets Bolshevist Alexis Minski at her grandfather's bookstore. After Ruth complains to her superintendent about undernourished schoolchildren, Minski's ravings cause her suspension, and she joins the Reds. Meanwhile, Captain Nathan Levison, returning from the Argonne, is assigned by the Secret Service to investigate New York's radicals. While visiting the Carrolls to announce the imminent arrival of Ruth's brother Davy, who saved Levison's life but lost his foot, Levison falls in love with Ruth. Chagrined, Minski convinces Ruth that Levison plans to arrest her and her grandfather, whereupon Ruth furiously requests that Levison be killed. After Governor Alfred E. Smith signs a bill making it illegal to display the Red flag, the Bolshevists plot to assassinate him, the Mayor of Seattle, and Attorney General Alexander Palmer, but Davy, with other soldiers, break up the meeting. Davy convinces Ruth of Minski's perfidy, and they save Levison. Ruth marries Levison, and at a wedding attended by the governor, Davy marries a reformed Bolshevist.