London, 1876. Tiny Hetty Feather is left at the Foundling Hospital, a refuge for abandoned children. Before she can start school, Hetty must live with a foster family in the countryside. Life there is tough, but with her foster brothers Jem and Gideon, she works in the fields and escapes into vivid imaginary games. Together, they sneak off to see the travelling circus, where Hetty is captivated by the dazzling Madame Adeline and her performing horses.
But happiness fades when Hetty must return to the Foundling Hospital, facing strict rules, awful uniforms, and terrible food. Missing Jem terribly, she clings to hope as a chance to find her real mother emerges. Could Madame Adeline be her? Or is the truth even more surprising?