Young magician Gywn and his friend Nia have been warned to stay away from Emlyn Llewelyn, the strange boy who claims his mother lives on the moon. And yet, a mysterious magic continues to draw them to him. But why? It's up to Gwyn and Nia to solve the mystery, with the help of Arianwen, the Snow Spider.

Gwyn can feel danger coming in the wind. Somehow he knows the warnings have to do with the broken toy horse that holds the evil spirit of a prince who lived long ago. When Gwyn discovers that the prince's dark soul has escaped from the horse and is seeking revenge Gwyn, Emlyn, and Nia have to figure out how to save the mysterious soldier who claims to be Nia's distant cousin. With the help of the Snow Spider, can they recapture the prince's soul without hurting the Chestnut soldier?