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

The Alden children help out a storeowner at the Hope Harbor Mall and discover that someone is tampering with the merchandise shipments.

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.

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.

While visiting a Navaho Indian reservation in New Mexico, the Aldens try to save a forest under threat of development by proving it is the site of a lost, buried village, but someone is sabotaging their dig.

The Alden children plan to ride in their boxcar at the Greenfield Founders' Day Parade, but the newly refurbished boxcar is stolen a couple of days before the big event.

The Alden children uncover a plot to sabotage the Greenfield Bears baseball team. Includes baseball puzzles and activities.

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

The Alden children investigate various mix-ups at a zoo run by their grandfather's friend in an effort to save it not only from pranksters but also from the town council.

"Henry, Jessie, Violet, and Benny used to live in a boxcar. Now they have adventures everywhere they go. At a lighthouse, the children find a mystery in the night!"--