The message in the hollow oak : Nancy Drew Mystery Series, Book 12

A group of professional detectives challenge Nancy to tackle a mystery that they have failed to solve: find an invaluable message hidden by a missionary centuries ago in a hollow oak tree in Illinois. While searching the woods for the ancient tree, Nancy and her friends live with a group of young archaeologists who are excavating prehistoric Indian burial mounds on a nearby farm. A shadowy enemy stalks Nancy and harasses everyone at the dig. The young investigator pursues her dangerous adversary to an outlaws’ cave, and is threatened when she discovers an unusual treasure. How Nancy, with few clues to go on, solves this complex mystery will thrill all readers. Nancy travels by train to Canada to inspect some land she has won in a lottery. She befriends an authoress who asks her to deliver a message to a long-lost love. Nancy has another mission -- fend off two men who have heard there is gold on her land, and are determined to get there first. Nancy Drew determines if an ivory elephant charm really protects its wearer from harm when she investigates the involvement of a member of the Bengleton Wild-Animal Show in a mysterious scheme. Nancy Drew tackles a mystery professional detectives failed to solve--finding a valuable centuries-old message in a hollow oak tree in Illinois