Haunting of Hillside School — Kristiana Gregory

Cabin Creek is a small town with a lot of big secrets.

When a girl's face appears, then disappears, outside a window of their spooky old schoolhouse, the cousins think they've seen a ghost. More strange clues -- piano music lilting through empty halls, a secret passageway, and an old portrait that looks like the girl from the window -- make Jeff, David, and Claire begin to wonder: Is their school just spooky, or could it be ... haunted?