Are you looking for a sex, crime, and murder mystery set in Regency England? I'm afraid you haven't found it. All that dates the book's story is the mention of 1819 at the beginning of the first chapter. After that, it just is a generic sex and crime story. Stone Devil Duke by K. J. Jackson is showing up major defects in writing without doing at least some minimal research.
It is always difficult to come second and later. When writing a biography, it makes your job as a writer that much harder and your research must be more thorough than that previously done. Still, the outcome might be a book that contains nothing new over what has already been written. It ends up being a rehash of well known and acclaimed books with no merit of its own.