The Moonstone Castle Mystery is the fortieth volume in the Nancy Drew Mystery Stories series.


When Nancy receives a valuable moonstone as a gift from an unknown person, she is amazed and puzzled. She soon becomes involved in a mystery involving the Bowens and their missing granddaughter which leads Nancy, Bess and George to Deep River. Investigating the haunted  Moonstone Castle leads to a connection between the castle and the mysterious, as well as the revelation of what happened to Joanie Horton.

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