When Nancy Drew receives a valuable moonstone as a gift from an unknown person, she is amazed and puzzled. But it is only the first of several startling events in this complex mystery that challenge the ingenuity of the pretty sleuth. Why are the Bowens – a missionary couple who recently returned to the United States – having so much trouble finding their missing seventeen-year-old granddaughter, Joanie Horton? Nancy and her friends travel to Deep River, the town where the young Jonie lived. From the motel where Nancy and her friends stay, they can see an intriguing castlelike structure with a drawbridge. Gossipy Mrs. Hemstead at the village tearoom insists that Moonstone Castle is haunted. Curious, the three girls attempt to explore the abandoned castle, but an ominous voice warns them away. Other strange happenings in Deep River convince Nancy that there is a connection between Moonstone Castle and the mysterious moonstone gift. But what is the significance? And where does the baffling disappearance of Joanie Horton fit into the intricate puzzle?

When Nancy Drew receives a valuable moonstone as a gift from an unknown person, she is amazed and puzzled. But it is only the first of several startling events in this complex mystery that challenge the ingenuity of the pretty sleuth. Why are the Bowens – a missionary couple who recently returned to the United States – having so much trouble finding their missing seventeen-year-old granddaughter, Joanie Horton? Nancy and her friends travel to Deep River, the town where the young Jonie lived. From the motel where Nancy and her friends stay, they can see an intriguing castlelike structure with a drawbridge. Gossipy Mrs. Hemstead at the village tearoom insists that Moonstone Castle is haunted. Curious, the three girls attempt to explore the abandoned castle, but an ominous voice warns them away. Other strange happenings in Deep River convince Nancy that there is a connection between Moonstone Castle and the mysterious moonstone gift. But what is the significance? And where does the baffling disappearance of Joanie Horton fit into the intricate puzzle?

Nancy's Aunt Eloise, aware of her niece's current interest in learning horseback riding stunts, sends her a second-hand golden bracelet bearing charms of horses in all five gaits; a sixth charm is missing. Coincidentally, the Sims Circus, former employer of Nancy's equestrian instructor, is coming to town. Nancy investigates the link between the unhappy circus star, young aerialist, Lolita, and her bracelet. Lolita is the adopted daughter of the acting manager, Ringmaster Kroon, and his wife. Pietro, the young, handsome clown, tells Nancy Lolita has the missing charm from her bracelet. Nancy's regular appearances at the circus, and her detective reputation brings the ire of Kroon. When a bareback rider is injured, Nancy is asked to join the show as her replacement.

When Nancy receives a letter informing her she’s heir to a fortune, she decides to track down the sender, as well as the other Nancy Drew.

When a series of rare-book thefts strikes the Bloom’s Bookstore & Coffeehouse in River Heights, Nancy Drew finds her only clue in the handwriting of a dead woman.

Nancy is given an aerial view of a burglar entering her home during a Honolulu vacation.