Why is the strangely clothed ghost child spying on Luke and his friends? Is this silent watcher linked in some way to the centuries-old riddle carved on the ancient stone fragment that the children discover? As the pals struggle to make sense of the strange happenings that engulf their summer vacation, they suddenly realize that they have stumbled upon a dangerous puzzle, right there in their own village. But others, too, are interested in solving the mystery, and the children have to race against time to uncover a long hidden treasure and the truth.