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.

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

While helping run Jerry Taylor's general store, the Alden children investigate his mysterious employee Nancy.

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

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

The Alden children draw upon their resourcefulness to save the neighborhood firehouse from being torn down, while they also face a series of mysterious incidents connected with it.

The Boxcar children uncover a mystery on a train trip from Boston to San Francisco.

While helping their grandfather prepare for Greenfield's Winter Festival, the Alden children uncover a mystery surrounding the statue in the town square.

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

The Alden children investigate the old boxcar where they used to live to find out if something that happened long ago is now haunting it.