|The Moonstone Castle Mystery|
|Series||Nancy Drew Mystery Stories|
|Publisher||Grosset & Dunlap|
|Media type||Print (Hardback & Paperback)|
|Preceded by||The Clue of the Dancing Puppet|
|Followed by||The Clue of the Whistling Bagpipes|
The Moonstone Castle Mystery is the fortieth volume in the Nancy Drew Mystery Stories series. It was first published in 1963 under the pseudonym Carolyn Keene. The actual author was ghostwriter Harriet Stratemeyer Adams.
When Nancy 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? Trying to uncover a clue to the orphan girl's whereabouts, Nancy and her friends travel to Deep River, the town where young Joanie Horton lived with her paternal grandmother until Mrs. Horton's death fourteen years ago.
Nancy, Bess, and George can see, from the motel where they stay, 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.
Later, when the friends are searching the castle, Nancy becomes separated from the others and is grabbed by a whiskered man. He holds a small bottle under Nancys nose and the fumes cause Nancy to swoon and she is dragged into a room. The others soon find her, but overcome by the fumes, Nancy has fainted. Ned carries Nancy outside where she soon revives, while the others hold the strange man.
Other strange happenings in Deep River convince Nancy that there is a connection between Moonstone Castle and the mysterious gift. But what is the significance? And where does the baffling disappearance of Joanie Horton fit into the puzzle?
How the young detective exposes a cruel hoax that has far-reaching results makes a dramatic story.