Franti, an organ grinder of the poor districts of New York, has a daughter, Isola, who sings to his street piano's accompaniment.

Clean-living pugilist Jim Fortune assists Angelica Hart when her husband Duncan assaults her in a Bowery café. Soon after, Jim fights a bout with Hart, an amateur society boxer, during a dinner party. Enraged by the sight of whip marks on Angelica's neck, Jim knocks Hart out soundly. In revenge, that night Hart attacks Angelica.

Dorothy Evans, a chemistry teacher at her aunt's girls school, hopes to satisfy her yearning for adventure when she vacations with her aunt, who desires to wear men's clothes, at a secluded island in the Chesapeake Bay. On the boat, they witness officers shooting an escaping prisoner diving overboard.

When Bob Stokes, a wealthy New York clubman, loses his fortune, he is jilted by his fiancée Marcia Fontaine. He then wanders to an upstate lumber camp where he impresses the owner, Henry Willard, with his leadership and fighting abilities. After Stokes quells a strike engineered by the previous foreman, Robert Brummon, who is really a Bolshevik agitator, to prevent shipments of lumber for government contracts, Brummon, seeking revenge, sets the forest on fire, but Stokes controls it. Willard then sends for Stokes to oversee his New York shipyards where a government "mystery ship" is under construction. After Stokes and Willard's daughter Helen fall in love, Brummon gets Marcia to attempt to seduce Stokes. Marcia lures Stokes to her apartment, where Brummon plans to kill him, but he escapes when he learns that a time bomb is set to destroy the ship.