In 1852, Emma and her mama board the Sally May for a steamboat journey filled with danger and adventure.

When concern over her beloved pony, Licorice Twist, lures ten-year-old Emma below the main deck--a place that she has been forbidden to go--she 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 develop a friendship that spans classes and ship levels.

When the boiler explodes and the steamboat begins to sink, Emma must fight her way through the black smoke to find her friends and family. But is it too late?