The Alden family rents a houseboat to drift down the river, and encounters a mystery in the little towns along the river, involving a fast black car.

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 Aldens try to help a visiting Russian gymnast who is surrounded by mysterious people and events and who seems to have a secret.

Henry, Jessie, Vioet and Benny Alden are brothers and sisters - and tehy're orphans. The only way they can stay together is to make it on their own. One night, during a storm, the children find an old red boxcar that keeps them warm and safe. They decide to make it their home.

At the same time that the Alden children's efforts to raise money for a new hospital wing are being sabotaged by nasty tricks, they find their attempts to befriend the new girl Beth frustrated by her strange behavior.

"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"--

A series of practical jokes at a restored nineteenth-century farmhouse makes the Aldens wonder if the ghost of its builder is at work.

When their favorite author fails to arrive as scheduled to speak at the local library, the Alden children investigate how he could board a train and never be seen again.

The four Alden children, aged six to fourteen, uncover a mystery while volunteering at a food pantry for the needy.