For a fleeting instant Maria thought she saw a little white horse with a flowing mane and tail, head raised, poised, halted in mid-flight, as though it had seen her and was glad.' The beautiful valley of Moonacre is shadowed by the memory of the Moon Princess and the mysterious little white horse.

When Maria Merryweather comes there on a visit she finds herself involved with an ancient feud. She is determined to restore peace and happiness to the whole of Moonacre Valley. And Maria usually gets her own way.