Go back and reread Lois Duncan sometime. It might not scare you anymore, and you see the plot twists a mile away, but her characters are psychologically real. And, like good horror, they are exagerrations of the real world--just look at "Daughters of Eve." I read some of those when I was older and was always impressed by how nuanced her characterization and how well she handles them. Sometimes the boorish jock does the right thing; sometimes the nerdy sweet girl does the worst.