An antique dealer's revelation about a former queen's priceless heirloom starts Nancy on a trail of exciting adventures.

Madame Alexandra, who is now living incognito in River Heights, asks Nancy to find her missing grandson. With only one clue to go on-a faded photograph of the prince at the age of four-the young detective begins her search, which rapidly involves her in a series of dangerous and harrowing adventures. When Nancy needs help, she calls on her friends, Bess, George, Dave, Burt and her boyfriend, Ned.

How Nancy's discovery of the heirloom's secret unmasks a slick imposter and reunites the long-separated family climaxes this suspense-filled mystery story.