Twelve-year-old Katie resents her beloved parents when they decide to move their family to the Yukon for Dad's new job. But when they take in six-year-old Siggi as a foster child, Katie is REALLY mad. She escapes from her unhappiness quite by chance when she realizes her pony, an Icelandic horse called Peggy, can fly--through time as well as space. By accident she takes Siggi to nineteenth-century England, where the two are adopted into a loving family. But when Peggy and Siggi are kidnapped and forced to work in an underground mine, Katie must rescue them or risk losing them forever. Through the danger and the triumph, and the connections she makes through time travel, Katie comes to understand the meaning of family.