The Hidden Staircase (Nancy Drew, #2) by Carolyn Keene, Mildred Benson (Ghostwriter)
Nancy resolves to help Helen Corning's relatives solve the mystery of the ghost haunting their old mansion. A mysterious man appears at the Drew home to warn Nancy that her father, Carson Drew is in danger. This warning prompts a search for the missing Willie Wharton, a land owner, who can prove he signed away his land to the railroad and save the railroad from a lawsuit. Meanwhile, the disappearance of Mr. Drew, thefts and mysterious goings on at Twin Elms, and the discovery of a hidden staircase lead Nancy to solve these baffling mysteries.
The story is based on the original title of the same name first published in 1930. The plot is vastly different in this extensively revised and shortened version.
Dog Gone Note: Although this is part of a series, it can be read as a stand alone. Both copies of this book are in excellent condition.