Mandie and her friends hear strange noises on a seemingly abandoned fishing boat in the harbor at Antwerp, Belgium, and wonder what the link may be between the boat and a man whom they believe to have stolen masterpieces from a museum.
After visiting with her Cherokee relatives, Mandie receives word from Jonathan Guyer about a mysterious secret, but when she tries to find him, she learns that he has fled to Long Island, so she decides to find out the secret for herself.
After some jewelry goes missing while Mandie and her friends spend some time at the Patton household, they must find out if the thefts and strange noises are caused by jewel thieves, or by ghosts.
When Mandie's and her grandmother's jewelry starts to disappear, Mandie is more anxious than ever to figure out the mystery. Who-or what-is in the house?
Upon returning from vacation, Mandie and her friends discover a large crack in the secret tunnel beneath her house that not only threatens to collapse the house, but reveals a mysterious and frightening cavern behind it.
Mandie is sure there is a mystery hidden behind the crack in the wall of a tunnel below her house.
Mandie's favorite teacher, Miss Hope, has gone missing.
During her summer vacation, Mandie learns that her beloved teacher, Miss Hope, has disappeared. Fearing Miss Hope will not be found before the new school year begins, Mandie and her friends mount their own search for the missing teacher.