An antique dealer's revelation about a former queen's priceless heirloom starts Nancy on a trail of exciting adventures. Madame Alexandra, 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 dangerous search. A secret in a jewel box helps unmask a slick imposter and reunites the long-separated family.