The Hidden Staircase
The Turnbull sisters, Rosemary and Floretta, ask Nancy to help them solve the mysterious “haunting” of their Civil War-era home, The Mansion.
The sisters explain that numerous valuables have gone missing but they cannot understand how anyone could have entered the locked house to commit the thefts.
Before Nancy sets off to stay at The Mansion for a week, she receives a threatening letter telling her to stay away from the Turnbull mystery.