I'm trying to identify a ghost story that I read in about 1976. It's set in rural America in the 1930's, and the main characters are a pair of young twins - one good, and one evil.
The boys discover (or inherit?) a cursed artifact, which the evil twin uses to cause accidents to anyone he dislikes - for example, another boy is impaled on a pitchfork while playing in a barn, and a woman who has a row with their mother falls down the stairs and breaks her neck. The evil twin is himself killed in an accident (I think he falls down a well, but I'm not certain), possibly caused by the artifact, and his ghost returns to haunt the good twin and persuade him to move to the "dark side".
I'm afraid I don't remember the ending. Any help you can give would be most appreciated.