Someone or something is making a mysterious tapping sound at midnight in the home of a famous inventor known for her one-of-a-kind clocks. There is an invention convention taking place in the home and the Alden children are competitors at the convention. Does the mysterious tapping mean trouble for the convention? The children are determined to find out.

The Alden children help out a storeowner at the Hope Harbor Mall and discover that someone is tampering with the merchandise shipments.

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

When their favorite author fails to arrive as scheduled to speak at the local library, the Alden children investigate how he could board a train and never be seen again.

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.

When Allie is contacted by the ghost of a dog, she and Dub investigate the surly new boy at school and his father, who may be running a puppy mill, to see if they are involved.