Night Whispers (Second Opportunities #3) by Judith McNaught

A policewoman in a small Florida community, Sloan Reynolds knows that her modest upbringing was a long way from the social whirl of Palm Beach, the world inhabited by her father and her sister, Paris. Total strangers to Sloan, they have never tried to contact her — until a sudden invitation arrives, to meet them and indulge in the Palm Beach social season.