The year is 1852. Ten-year-old Emma Wright and her mama have boarded the Sally May for a steamboat journey that will take them up the Mississippi River to the Missouri River and finally to St. Joseph where Papa will be waiting. The pair is being escorted by Dr. Burton, who is tending to Mama's fragile health.But Emma doesn't like that Dr. Burton treats her like a bothersome child and bosses her around. And she is used to getting her own way. When concern over her beloved pony, Licorice Twist, lures her below to the main deck—a place that she has been forbidden to go—Emma is shocked by what she encounters. Here is a world completely different than the pampered one above with its comfortable stateroom and fine food. Here livestock and poor immigrants huddle together—underfed, unclean, and exhausted.Soon Emma is making regular trips below, ferrying food to Patrick, an eleven-year-old stowaway who recently emigrated from Ireland. Slowly, Emma and Patrick...