When Sára hears a story about the mare Rosie, whose ghost is said to appear under the full moon, she begins to look forward to scaring her friends around the campfire with the story. But then the ponies in the pen start to get restless, as if they are afraid of something. Do they see what people don't see? Sara spots something big in the bushes, discovers strange tracks in the dust, and her pony opens the gate of his box, which Rosie says she did too. Is it possible that Sun Valley is being bypassed by a ghost?