When the Aldens go to the Pickering Natural History Museum to assist with the opening of a dinosaur exhibit, their work is hampered by a series of mysterious happenings.

When the Alden children help the curator of the Greenfield Museum set up a traveling exhibit of ancient Egyptian artifacts, the display seems to be undergoing a run of bad luck and the children wonder whether it might be under a curse.

When the Alden children go camping on Blizzard Mountain, a place said to be inhabited by a ghost looking for buried treasure, they begin to think someone or something is trying to scare them off.

While staying at the Crooked House, the family home of their housekeeper Mrs. McGregor, the Aldens try to solve a riddle that will lead them to a hidden treasure.

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

The Aldens investigate when the arrival of several suspicious characters in Greenfield coincides with a mystery involving a popular boy actor.

The Alden children discover another mystery when they agree to help injured Mr. Yee tend to his plot in the community garden and find out that vegetables are going missing and plots are being vandalized.

Four orphaned children make a home for themselves in an abandoned boxcar and are united with their grandfather.

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

"The Alden children discover clues that could help them figure out why a man vanished from a run-down yellow house on Surprise Island"--