When the Alden children go camping on Blizzard Mountain, a place said to be inhabited by a ghost looking for buried treasure, they begin to think someone or something is trying to scare them off.

The Boxcar children uncover a mystery on a train trip from Boston to San Francisco.

Someone or something is making a mysterious tapping sound at midnight in the home of a famous inventor known for her one-of-a-kind clocks. There is an invention convention taking place in the home and the Alden children are competitors at the convention. Does the mysterious tapping mean trouble for the convention? The children are determined to find out.

The Aldens start a business producing birthday parties and find themselves investigating a series of robberies taking place during their parties.

The Aldens become involved in a community theater production of "The Wizard of Oz," which is systematically and mysteriously being sabotaged.

When they help out at a guide dog training school, the Alden children meet several people who seem obsessed with a particular dog named Ginger.

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

While visiting Lake Lucille in the Adirondack Mountains, the Aldens hear stories about a monster in the lake and then encounter evidence that it may be real.

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 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.