One warm night four children stood in front of a bakery. No one knew them. No one knew where they had come from. Henry, Jessie, Violet and Benny are orphans.They discover an old red boxcar that provides them shelter from the storm.

"The Aldens spend the summer on Grandfather's island! Joe, the island's friendly handyman, helps them with anything they need, but as the children continue to explore their summer home, they realize there is more to the island--and to their new friend--than meets the eye."--Publisher's description.

Henry, Jessie, Benny, and Violet Alden meet Mike Wood and a strange chain of events begins. Mike's house is mysteriously burned down, a man in a blue hat appears, and the Alden's uranium mine is in danger of being sabotaged. The four youngsters solve the mystery.

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.

The boxcar children travel to Maine, take canoes into the wilderness and live in a house exactly like the one on Surprise Island, except the Maine house is brown, not yellow. They untangle the mystery of the two houses. Relates the exploits of the four Alden children as they locate a missing man. The Boxcar children are determined to solve the mystery that surrounds an old yellow house on their grandfather's property. Strange things have happened...

The Alden children, isolated in a storm at a small bus station, are led into a mystery centering on a polluted river.

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.

Henry, Jessie, Violet, and Benny hav3e promised Grandfather a vacation from mysteries during their island visit. But the romise proves hard to keep when things start to go missing. Then an old fisherman tells Benny of the island's ghost horse, and late that very night benny sees a mysterious stallion galloping down the beach. Could the ghost horse have something to do with the disappearances?

When the Alden children and their grandfather visit Everglades National Park in Florida to solve the mystery of a missing ranger, they discover that a panther provides a clue.

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.