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 in that house where long ago a man disappeared.

The children are spending the summer on their own private island but there is a mysterious stranger on the island.

The entire town of Yellow Sands is left puzzled by a mysterious fire.

A young Canadian visitor helps the Alden family solve a mystery involving a lost coin collection.

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.

Six children help solve the mystery of a missing spyglass that has kept two brothers feuding for years.

When the Aldens visit a university campus, they must solve a mystery involving an old library whose stone gargoyles seem to move on their own.

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

The Alden children hunt for their late grandmother's necklace that has been missing for years.

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