Grandpa Alden tells Henry, Jessie, Violet and Benny of the curious circumstances in which the yellow house became vacant over forty years ago. Determined to solve the mystery, the children uncover a trail of clues that leads them to memories of their boxcar days.

While exploring the caves around Dragon's Mouth Cavern, a series of unusual and somewhat frightening events convinces the Alden children that someone does not want them around.

When the Alden children accompany their grandfather to the Snow Haven Lodge, a series of odd occurrences threaten to disrupt the annual winter games.

While staying at a hotel in New York City, the Aldens investigate a series of annoying pranks plaguing the management and guests.

Two brothers take summer jobs at a department store where a series of peculiar events brings them under suspicion.

The Aldens, while testing the latest version of their favorite computer game, are surprised to find messages directed specifically at them.

Henry, Jessie, Violet, and Benny--four children who used to live alone in a boxcar and now reside with their grandfather--arrive at Camp Seagull overflowing with excitement, but they soon realize that some of the other campers are not above cheating in the annual camp Olympics.

The Alden children search for buried treasure on Blizzard Mountain, but a mysterious rival treasure hunter is determined to chase them off the mountain.

The mysterious disappearance of a reclusive neighbor's cat involves the Boxcar children in some complicated detective work.

While staying at the Crooked House, the family home of their housekeeper Mrs. McGregor, the Aldens try to solve a riddle that will lead them to a hidden treasure.