What is the main problem in Nancy drew the hidden staircase?

In "Nancy Drew: The Hidden Staircase," the main problem revolves around Nancy investigating mysterious occurrences at the home of her friends, the Turnbulls. They believe their house is haunted, as strange noises and unexplained events disrupt their lives. Nancy's goal is to uncover the truth behind these incidents, ultimately leading her to discover a hidden staircase that reveals deeper secrets. Her adventure highlights themes of bravery, curiOSity, and the pursuit of truth.