Continuing the story in which Tamzin Weston and her guardian pony Moonlight confront the evil spirit of the Grey Horse.

Tamzin and her new friend Marga are preparing for the pony Fun Day. But there something suspicious about Marga and her pony Lossie. First Marga takes Tamzin's protective blue talisman. Then Marga schemes so that Tamzin has to ride Lossie in the parade.

Lossie bolts and heads for the cliffs with Tamzin clinging on. She almost falls over the edge but Moonlight rescues her just in time. Marga and Lossie suddenly disappear into thin air. They are agents of the Grey Horse and, according to legend, Tamzin knows he'll be back for her...