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

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.

While vacationing at a friend's country home, the four Alden siblings try to find a long-missing, priceless brooch and investigate the existence of a ghostly stream.

While visiting a recent purchase of Grandfather's, a ghost town in the Rocky Mountains, the Aldens encounter a mystery involving a run-down motel and a woman who may be a ghost.

While visiting a small town in Alabama, the Aldens hear mysterious howls at midnight, leading them to wonder if an old local legend about a ghost dog is true.

When their grandfather arranges for them to spend two week at Sunny Oaks, the four Alden children enjoy settling into the routines of farm life but become suspicious about a mysterious horse locked in the stables.

Can the Aldens figure out who's responsible for the bad press before the center gets shut down for good? Henry, Jessie, Violet, and Benny are excited to learn more about raptors when they volunteer at a rehab center for wild birds. But not long after they arrive, a series of strange events makes it seem like someone might be trying to sabotage the center. Who could the culprit be, and why would they want to cause trouble for injured birds?

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.

While spending two days touring a zoo to see the baby animals, the four Alden children, aged six to fourteen, help catch an escaped monkey, participate in a photography contest, and investigate a missing camera.

"Jessie and Benny are participating in the Great Greenfield Bake-Off, a local baking competition for kids. But ingredients get mixed up during the competition and then the power goes out. Is someone trying to put an end to the contest?" -- provided by the publisher.