The Curse of Penryth Hall by Jess Armstrong
The Curse of Penryth Hall is engrossing. Ruby, our protagonist, is a disgraced heiress living in exile in Exter. There she works for her landlord, Mr. Owen, who sells rare books. Ruby is jaded, drinks too much, and is rather reckless. She's also generous and stubborn. As the book opens, Mr. Owen sends her with a box of books to a small village in Cornwall. The books, it turns out, are for Ruan Kivell, the town's Pellar, a wise man/witch/folk healer character. After making her delivery she stops a Penryth Hall to visit Tamsyn, an old friend with whom she has a complicated history. It's clear at dinner that Tamsyn's husband is not a good man. The reader is not surprised when he ends up dead the next morning, a victim of "the curse" according to the locals. Ruby doesn't believe in curses, but she does believe in protecting her friend and uncovering the truth.
Cornwall is a superstitious, suspicious place still...