I.M. Mann, millionaire president of a large corporation, is known as "the man with the iron heart." James Boyd, cashier for Mann's corporation, is delayed one morning because of a dying mother, and is discharged. Then Boyd goes to Union headquarters with his story. The thousands of workmen employed by Mann finally reach the limit of endurance, and at a union meeting, resolve to demand increased wages, a cessation of child labor and other benefits, or strike. He refuses to hear a committee of workmen and says, "I'll close up the factories and let you starve."

When the United States enters World War I, the widowed Helen worries that she will lose her only son David, who has just turned 21. Although David patriotically urges the employees at his factory to enlist, he reluctantly gives in to his mother's pleas to remain at home with her. When David is drafted, his panic-stricken mother alters the date on his birth certificate, although the later birth date implies that he is illegitimate. Disgusted, David enlists under an assumed name, thus shaming Helen, who confesses her dishonesty to the townspeople. Her son, now in uniform, then forgives her.