The children and their grandfather spend the summer traveling on a train--in their own caboose.

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.

A family, snowbound in a vacation cabin, discovers adventure in surrounding wild life, three children they find in the snow, and a search for a lost recipe.

The Aldens become involved in a community theater production of "The Wizard of Oz," which is systematically and mysteriously being sabotaged.

The Aldens investigate when the new coach of their community basketball league has her Most Valuable Player trophy stolen.

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 an elderly friend is injured, the Alden children offer to help him with his window-washing business in their small town of Greenfield and agree to help him solve a riddle that has arrived in a mysterious invitation.

The Alden children are thrilled when a famous orchestra comes to their town to perform, and when an original Mozart score turns up missing, they solve the mystery of its disappearance.

When the Alden children accompany their grandfather to the Snow Haven Lodge, a series of odd occurrences threaten to disrupt the annual winter games.

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.