I think that the situation is a bit odd, but I remember from AF's introduction to a Girls Gone By edition (pretty sure I don't have it with me) that the idea for the book started after a friend of AF suggested that Karen might marry a don,and AF thought about that and decided that, given some conflict and edginess, it might make a good idea for a book. I'm pretty sure I remember her saying that the conflict was going to originally come from him being a wife-beater, before deciding that would be going too far. Edwin remains an oddly conflicted character though - I read an earlier post on this web-site which said that earlier versions of Run Away Home had him beating Rose and Charles. Presumably he does have some fatal charisma for Karen - and he is shown as being intelligent and witty when he wants to be.