Challenging questions confront Nancy Drew when she attempts to solve the mystery of the strange tapping sounds in the house of a retired actress. Who is the tapper? How does he gain access to Miss Carter s house, despite securely locked doors and windows? Why do the tapping sounds come in Morse code? Is there a sinister motive behind the prowler s actions? While trying to learn the answers to these and other puzzling questions, Nancy finds her investigations complicated by the dishonest administrator of a will and by a thief who steals the actress s prize Persian cats."