The Moonstone Castle Mystery

Infobox Book |
name = The Moonstone Castle Mystery


image_caption =
author = Carolyn Keene
country = United States
language = English
series = Nancy Drew stories
genre = Detective, Mystery novel
publisher = Grosset & Dunlap
release_date = 1963
media_type = Print (Hardback & Paperback)
pages =
isbn = NA
preceded_by =
followed_by =

"The Moonstone Castle Mystery" is the fortieth volume in the Nancy Drew mystery series. It was first published in 1963 under the pseudonym Carolyn Keene. The actual author was ghostwriter Harriet Stratemeyer Adams.

Plot summary

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? 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. Henstead 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 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 and exciting story.