The Boxcar children investigate the disappearance of a student's research paper from an observatory and the subsequent disappearance of another student.

The Alden children visit a family friend at his apple orchard which is rumored to be haunted, but instead of a ghost they find that some of the families' valuable antiques are being stolen.

While visiting Chicago with their grandfather, the Alden children begin receiving mysterious clues to a treasure hunt. Includes related puzzles, games, and activities.

While visiting a recent purchase of Grandfather's, a ghost town in the Rocky Mountains, the Aldens encounter a mystery involving a run-down motel and a woman who may be a ghost.

While the Aldens are visiting a friend of Grandfather's at the beach, Benny finds a long-lost piece of a map to a legendary pirate treasure, a discovery that brings unwanted attention from fortune hunters.

The Aldens accompany their grandfather to his class reunion and investigate the possibility of a buried Civil War treasure, and of a ghost in the bell tower, at Goldwin University.

When an elderly friend is injured, the Alden children offer to help him with his window-washing business in their small town of Greenfield and agree to help him solve a riddle that has arrived in a mysterious invitation.

When the Aldens have the chance to work at a candy factory, they try to find out who is sabotaging the candy and why.