To Love for Ever — Janet Cookson

Private detective Kate Rivers is asked by consultant Brad Stevens to search for his business partner, Virginia Ashton, who has disappeared whilst working for the Stratton twins, who own a stately home in Berkshire. In spite of the hostility of her boyfriend James, Kate goes to Stratton Park, posing as Brad's assistant. Following Virginia's trail, she unearths a shocking family secret. She also finds the search begins to involve her own feelings - for the man who has hired her...