The Boxcar children uncover a mystery when they compete in several contests at the county fair.

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.

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.

When the Aldens go to the Pickering Natural History Museum to assist with the opening of a dinosaur exhibit, their work is hampered by a series of mysterious happenings.

When the Aldens visit Yellowstone they discover a map showing the way to an old cabin where gold is supposedly hidden, but they encounter lots of interference in their attempts to hike the trail.

Four orphaned children make a home for themselves in an abandoned boxcar and are united with their grandfather.

The Aldens investigate when an old wooden mask they have found is stolen.

At the same time that the Alden children's efforts to raise money for a new hospital wing are being sabotaged by nasty tricks, they find their attempts to befriend the new girl Beth frustrated by her strange behavior.