The Hidden Staircase (Nancy Drew #2), Carolyn Keene

Writer: Midred Wirt (1930). Revised By: Harriet Stratemeyer Adams (1959). Nancy's friend, Helen, and Helen's great-aunt Rosemary ask Nancy to solve the mysterious happenings at her great-grandmother's mansion, Twin Elms. Nancy feels so excited to investigate the mystery until she hears that her father is being threatened by crooked lawyer…