Paul and Maureen Beebe's determination to own a pony from the herd on Chincoteague Island, Virginia, is greatly increased when the elusive Phantom and her colt are among the ponies rounded up for the yearly auction.
In 1847, when her mother's remarriage sends them on a difficult journey to California, Willow is swept overboard fording the South Platte River and must survive and search for her family.