Mary Wilkins and Anna Dewar were inseperable. They had grown up together, gone to school together, learned to ride together on Anna's horse September. Mary thought things would never change. But Anna's father had plans for her - plans that included sending her away to snobbish Kilmingdean School.

Anna promised to write, but her letters soon dried up. Mary, left behind, was forced to watch as Mr Dewar crippled September through over work, and could do nothing.

But, when it finally seemed as if Mary would lose both Anna and September completely, she embarked upon a daring scheme to rescue September and win back the respect and friendship of Anna and her father.