Who is James Fortescue from The Favored Child and what is their importance?

James is Marianne's brother and the man Julia is engaged to marry. When Julia first meets him, he amazes her when her sister refers to Dr. Phillips and James says, "Quack," repeatedly. James is with Julia when she meets Jimmy Dart, a boy who grew up in Wideacre but was enslaved as a child. Though she doesn't know Jimmy, she suddenly knows that she'll take him home with her.