How does the author use foreshadowing in Petals on the Wind?

In Part I, Christopher shows the reader that he is still in love with his sister, as the reader witnessed in the first book of this series. Christopher confesses that he will never love anyone else and only wants to be with Catherine. This places Catherine in a difficult position because she believes that incest is a sin. Catherine hopes that Christopher will get over her when he begins dating other girls, but Christopher insists this will never happen. This situation foreshadows difficulties between these two characters and suggests tension that will remain until this situation is resolved one way or the other.