Nancy receives a moonstone as a gift from an anonymous person. Mr. Drew enlists Nancy to help him with his latest case. The Bowens, a missionary couple, have recently returned from Africa and have been looking for their granddaughter without success. The girl went to live with her other grandmother in the town of Deep River after the deaths of her parents when she was a baby. However, the grandmother died shortly after that and all trace of the girl has been lost. When the girls arrive in Deep River they see Moonstone Castle in the distance and decide to explore it. This was a very boring book with a dull mystery and almost zero action. The summary in the book suggests that the castle is haunted, but that is never really mentioned in the book itself. Nancy doesn't do any brilliant detective work to find the missing girl, instead she basically stumbles upon her. I'd only recommend getting this book to complete your set.