He may look like a mild-mannered detective, but Inspector Gadget is somewhere between a man and a machine, and he's out to clean up the city if he can keep all his many parts under control.

Harriet is probably the most accomplished 11-year-old spy. She dreams of being a writer and her nanny told her to start by writing down everything she sees. It's all in good fun, that is until her friends find her private writings. Now they don't like Harriet much. Can Harriet win back her friends or is she doomed to be considered an outsider, a rejected writer and forgotten spy?

Four sisters, as different as the cities they were named after, return home to mourn their mother's alleged suicide and discover a secret that could tear them apart.