Lily's Ghost - Sheoaks Equestrian School, #3

Hattie stared across the paddocks to where Ghost was watching Lily who was looking back as if she'd never seen another white pony before. 'Something odd is going on here, ' she said quietly. The Hospital Horse Heroes, three miniature horses, come to stay at Sheoaks Equestrian School. Jimmy and Turtle are tiny Shetlands, but Ghost is a Welsh Mountain pony like Lily. Mystery surrounds the family that owns them, especially around Tom, the quiet little brother.
Where did Ghost come from? Why does Tom have such an attachment to her? What has Lily got to do with Ghost?