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.
"Let's have Laura Linney back"
Blue bells will be singing horses! This strange message, attached to the leg of a wounded homing pigeon, involves Nancy Drew in a dangerous mission. Somewhere an elderly woman is being held prisoner in a mansion. Nancy is determined to find and free Mrs Eldridge. While working on the case, the young detective's close friend, Helen Archer, begs her to solve a weird mystery.
"Not Laura Linney"
While solving the mystery of an old man's disappearing fortune, Nancy ends a family feud and reveals the identity of an orphan of unknown parentage.
"Please bring back Laura Linney (narrator)!"