I went through a Walter Scott phase as a pre-teen. The novels, not the poetry. I never could hack the poetry.
If you like RLS I'm sure you've read "Kidnapped" (Alan Breck is another one of your good/evil characters, though more good I think) but have you read the sequel ("David Balfour" in America, "Catriona" in Britain). A political thriller with asides into Scots folklore. The Lord Advocate Prestongrange is the good/evil character there (Sim Fraser and his mirror image Tod Lapraik being 100 percent evil!) "He was kind to me as any father, yet I ever thought him as false as a cracked bell."
I read “Kidnapped” quite a few years ago. Not only Alan Breck Stewart but the Captain and the ship’s drunken brute of a quartermaster or whatever his title was, have dual personalities.
Even David Balfour’s miserly Uncle isn’t all bad. I liked all the Disney movies based on Stevenson’s books. Of course Dr. Jekyll and Mr. Hyde are the ultimate dual personalities.