The Alden children draw upon their resourcefulness to save the neighborhood firehouse from being torn down, while they also face a series of mysterious incidents connected with it.
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.
When the Alden children set out to solve a jewelry store robbery, they find they must also deal with a mysterious thief who steals their favorite cereal.
While on a cruise with their grandfather, the Alden children help discover who is behind the mysterious troubles of the ship--disconnected phone lines, engine trouble, a man overboard--and still have fun sightseeing, eating, and swimming.
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.
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.
While visiting the seaport town of Ragged Cove, Massachusetts, the Alden children find the ship's log of the Flying Cloud, shipwrecked in 1869, supposedly during a mutiny.
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.
The Boxcar children investigate the disappearance of a student's research paper from an observatory, and the subsequent disappearance of another student.