The Mystery of the Empty Room — Augusta Huiell Seaman

After the death of their father, two sisters come to New Jersey to live with an uncle they never knew existed, and discover that Uncle Si, who sells antiques and second hand furniture, lives in a run-down but gracious old house, which harbors many mysteries -including one room which is kept locked and empty.

…the furtive footsteps drawing nearer…and NEARER!

Close to the wall Jean crouched, clutching her hammer in her hand. The unknown person was now advancing… Who is the intruder?