The Alden children have another mystery to solve when they visit a castle and must figure out which of the guests has stolen the Stradivarius violin.

The Alden children travel on a Mississippi paddle-wheel steamer to visit an old family friend in his cabin near Hannibal, Missouri, and try to discover who is responsible for the mysterious activities near the house.

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.

While helping fix up the old house their cousins have bought, the Aldens hear stories about its being haunted and find evidence suggesting that there may be a ghost there.

The Alden children are thrilled when a famous orchestra comes to their town to perform, and when an original Mozart score turns up missing, they solve the mystery of its disappearance.

While visiting the Florida Keys, the Aldens encounter suspicious characters, strange incidents at night, and a plot to steal valuable coral.

Henry, Jessie, Violet, and Benny are given the opportunity to be extras in a movie about the Alamo, but they are called upon to use their sleuthing skills when Claire, the star of the film, is implicated in the theft of a valuable ring.

When Grandfather's friend Seymour Curtis invites the Alden family to spend some time at his apple orchard, Benny is determined to find the ghost rumored to haunt the premises. Yet, it seems as if the Aldens may have a more earthly crime on their hands.

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.

The Boxcar Helpers baby-sit, wash cars, mow lawns, and care for pets to raise money for Greenfield hospital. But Beth keeps disappearing and other things start to go wrong. Is someone trying to put them out of business?