Nancy's father Carson Drew enlists her help in tracking down a missing heiress, and Nancy, Bess and George stumble upon a mysterious moss-covered mansion. They later hear that someone was murdered near the mansion and they hear strange noises coming from inside. The volume is 25 chapters in length, and includes a great deal of action, including a murder, gypsies, a missing heiress, a needy elderly lady, a reclusive artist, an airplane accident, and a forest fire.