The Password to Larkspur Lane (Nancy Drew, Book 10)

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, and  Nancy is determined to find and free her. Meanwhile, the young detective’s close friend, Helen, begs her to solve a second mystery. Helen’s grandparents, the Cornings, are frightened by a sinister wheel of blue fire that appears after dark in the woods outside their home at lonely Sylvan Lake. When Nancy discovers the significance of the eerie signal, she also learns that her two mysteries are connected.

Carolyn Keene is a pen name used by a variety of authors for the classic Nancy Drew Mystery series. The first author to use the pseudonym was Mildred Wirt Benson, who wrote 23 of the original 30 books. Other writers who have adapted the "Carolyn Keene" moniker include Leslie McFarlane, James Duncan Lawrence, Walter Karig, and Nancy Axelrod.