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.
Power of the Heir's Passion by L. R. W. Lee is a sort of a prequel to the Andy Smithson series. I assure you that this is the most accurate description of afterlife available, for the world of Oomladee, not ours. It is subtitled A Novella; not quite a book but too long for a short story. And it's a ghost story from start to end.
The Stolen Kingdom by Ross Rosenfeld is a very unhappy book, or maybe an unfortunate one. It definitely suffers from multiple personae disorder. It tells the story of the missing prince in a new way; the story is placed in an imaginary Europe without giving away any cultural details as to where exactly it is.
In book 4 of the Andy Smithson series, Phoenix, Arizona, receives visitors from Oomladee for a change. Resurrection of the Phoenix's Grace by L. R. W. Lee sees the conflict crossing the magical border before Andy's Mom sends him back to Oomladee when the situation at home gets out of hand and way too dangerous.
Book 3 in the Andy Smithson series sees our hero return to foggy Oomaldee after having been sent home to this world at the end of book 2. Disgrace of the Unicorn's Honor by L. R. W. Lee is another offering in fairy creatures and wild places that need exploring in a quest. It is no let-down compared to the previous two books.