Summer vacation on an almost private island gives the Aldens a challenge. Henry, Jessie, Violet and Benny used to live alone in a boxcar. Now they have a home with their grandfather and are spending the summer on their own private island. There is a mysterious stranger on the island with a secret--but that's not the only surprise in store for the Boxcar Children.

The Alden children suspect someone of trying to sabotage the local dog show.

"The Alden children are fixing up an old castle that will be turned into a museum, but they have to solve the mystery hidden within the castle's walls"--

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.

Benny wants adventure and finds it as he and the other Alden children help uncover the plan of those who would prevent ballooning from coming to Lloyd's Landing.

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

The Alden children investigate when Mrs. Murray's jewels are stolen during a party for the Starlight Skating Troupe.

Henry, Jessie, Violet, and Benny think the new neighbors are hiding something, because of their strange house and a gate decorated with spiders.