Polly Eccles is a "ragged girl" living in a dank slum who is responsible for her sickly four-year-old brother, Billy. After a doctor advises that Billy needs a healthier climate to recover, Polly packs their few belongings and decides they will walk to California. While hitchhiking along the way with their dog, the siblings are given a lift by Kirk Drummond, a young man who happens to be driving to California himself. Upon arriving, Kirk’s wealthy father, John Drummond, is initially horrified by his son's association with the "ragged" travelers. However, the story follows Polly’s trials as she attempts to navigate this new world and ensure her brother's health.