Charlie's horse, Phantom, has become tricky to ride, and when he bolts one day Charlie is left injured. To make matters worse, strange things are happening at the yard - tack is being moved and animals let out of the field. The Pony Detectives suspect that someone might be sneaking in and meddling, but can they discover exactly what's going on before things get out of hand? The fourth book in the adventure-filled PONY DETECTIVES mysteries.