After her overprotective grandmother has a stroke, Maya, an orphan, leaves her extremely restricted life in California to stay with her mother's family on a remote Wyoming ranch, where she discovers a love of horses and encounters a wild mare that her mother once rode.

Lost in the Black Forest, Otto meets three mysterious sisters and finds himself entwined in a puzzling quest involving a prophecy, a promise, and a harmonica. Decades later, as the second World War approaches, the lives of three children -- Friedrich in Germany, Mike in Pennsylvania, and Ivy in California -- become interwoven when the very same harmonica lands in their lives. All the children face daunting challenges: rescuing a father, protecting...