In St. Louis, renovations are about to begin on the News Boys' Home and Protectorate. Fred Carver approaches the sidewalk crew about to rip up the pavement out front, and asks that they preserve a slab of concrete that bears two sets of footprints: his own as a boy, and those of Father Dunne [Pat O'Brien]. The workers do not know who Father Dunne was, and Carver begins to relate the tale of the late priest and the creation of the building they stand in front of.
In 1905, St. Louis newspapers employ young boys, many of them orphans, to deliver papers. One brutally cold morning, one homeless boy falls ill and can't work. His two friends, Tony and Jimmy, go to Father Dunne's parish and tell the priest of their concerns. Father Dunne accompanies the two youths to where their friend lives: in a cardboard box. After he takes the three boys to his sister Kate Mulvey [Ruth Donnelly] and her husband Emmett [Charles Kemper], they agree to take the boys in on a temporary basis until a more permanent solution can be found.
Dunne visits his Archbishop John Joseph Glennon and tells him of his intent to build a home for the newsboys and other street children. The Archbishop pledges to support Dunne's efforts, but makes it clear that the diocese is not in a financial position where they can contribute any money to the project. Undaunted, Father Dunne uses his winning personality and gifts of persuasion to cajole, harangue, and otherwise convince local business people to support his project. Using donations, Dunne rents a run-down townhouse, and begins to refurbish it, again convincing local businesses to donate the materials for the renovation. He also enlists the help of a local attorney, Thomas Lee [Harry Shannon] to help him in his negotiations, as well as providing free legal counsel.
As the house gets more and more fixed up, the number of youths staying there grows. In addition to providing them food and shelter, Father Dunne also provides guidance to the young men, attempting to help them turn into productive members of society. Dunne particularly works hard on one of the more sullen, violent youths, Matt Davis [Darryl Hickman], who has been physically abused by his alcoholic father. Eventually, Dunne becomes aware that the adolescents under his care are being violently bullied by some of the older teenagers who also compete in selling papers. He at first attempts to talk to the manager at the paper in charge of sales, but his efforts are frustrated. Matt then organizes the boys at the home to work as a group, in support of one another, in order to offset the larger, stronger teenagers. While it is initially successful, the violence begins to ratchet up, eventually leading to a violent confrontation which sees the horse which has been loaned to the boys to help them deliver the papers killed, and Jimmy's leg is crushed under a wagon wheel. Matt blames himself for the altercation, and flees the home in shame.
Father Dunne then convinces Michael O'Donnell [Arthur Shields], who had loaned the boys the horse, to threaten to evict the newspaper from their building, since he owns it. The newspaper then relents and intervenes on the boys' behalf with the older delivery boys, averting further violence. Dunne then turns his efforts into raising money to build a larger, more permanent home for the boys. While he is doing that, he also continues to search for Matt. He eventually finds him, but cannot convince to him to leave his abusive father and return to the home.
Eventually, O'Donnell and Lee help Dunne form a board of directors to help raise money for the permanent home, and it is eventually built. After it opens, Matt arrives to ask for help from Dunne. He is fleeing from the police, after having almost been caught during a robbery. Dunne agrees to help him, but convinces him that the first step is to turn himself in. Before he can, however, they are surprised by a police officer. Matt mistakes him for his drunken father and shoots him, killing him.
Matt surrenders, but is sentenced to death. Even though Dunne intercedes on his behalf with the governor, the execution is carried out. While he was unsuccessful with Matt, Father Dunne gets solace from the boys waiting for him when he returns to the home, all of whom he has saved.
