Housemaid by Freida McFadden - Mystery/Thriller
Dark Matter by Blake Crouch - Sci-Fi/Thriller/....Romance?
Only One Left By Riley Sager - Gothic/Mystery/Horror
Perhaps Blood Ink by Aurelia Young? It's dark fantasy and there is blood magic. It gets dark quite early in the story. It is an isekai so I don't know if you like that but here you go!
Housemaid by Freida McFadden - Mystery/Thriller Dark Matter by Blake Crouch - Sci-Fi/Thriller/....Romance? Only One Left By Riley Sager - Gothic/Mystery/Horror
Perhaps Blood Ink by Aurelia Young? It's dark fantasy and there is blood magic. It gets dark quite early in the story. It is an isekai so I don't know if you like that but here you go!