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.

The Alden children start out on a one-day mountain climbing excursion that becomes very exciting. They unearth some mysteries and some treasure and have a good time in the process.

"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!"

While on a bicycle trip to their aunt's farm, the four Aldens help solve a mystery.

"Henry, Jessie, Violet, and Benny are spending the summer on a houseboat! Throughout the journey, the children have the feeling they're being watched-- and they are. Someone wants something on their boat, and he'll stop at nothing to get it. Can the Boxcar Children figure it out what it is before it's too late?"--P. [4] of cover.

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

At an old library, the Alden children discover a boy who needs their help and a stranger who is after a valuable object they found in the library.

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 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.

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.