We can she how Rose grows on this book, especially when she loses a close friend and consider herself guilty for his death. Dimitri shows a different side of him, more friendly towards Rose and their 'friendship'.
We also see Rose's mother Janine and understand more why she chose to raise Rose that way. And why Rose fells like she'd been abandoned by her mother. It's a choice: career or family. One that Rose has already made by being Lisa's guardian.
On the side there is Lisa and Christian relationship evolution, especially with some steamy scenes. They grow up alone and I can understand that they see each other like a soul mate.