When the Alden children join a group of volunteers to fix up an old house for senior citizens, they try to explain the puzzling behavior of their coworkers as well as investigate some unusual events.
While visiting a Navaho Indian reservation in New Mexico, the Aldens try to save a forest under threat of development by proving it is the site of a lost, buried village, but someone is sabotaging their dig.
The Alden children visit an old Kansas inn that is full of secrets, such as why did a famous photographer visit the innto take a single picture, who was the legendary guest who came west on an orphan train.
When a professional hockey player comes to Greenfield with plans to build an ice skating rink, the Alden children suspect that someone in town wants to stop the project.
The Alden children agree to help their neighbor search for treasure she believes is hidden in her attic, but the quest becomes urgent when they realize that someone else is trying to find it first.
While visiting their cousin's pineapple plantation in Hawaii, the Aldens hear a local legend about a black pearl with a curse on it and investigate mysterious incidents on and around the plantation.
