Jennifer Archer - The Shadow Girl (2013)

Lily Winston has a voice in her head - it belongs to Iris. They've been together forever and now Iris is pushing Lily to find out the truth about their past. To solve the mystery of why they exist and how Lily can remember things that Iris did before she was ever born. Is Iris a ghost? Is Lily possessed?

I don't want to spoil the book for anyone, so I can't really explain more than that. It was an interesting book and it raised a lot of questions in my mind. Mostly about whether souls exist or the mind just creates a personality? Also, is who we are a part of every cell in our body? What does this mean for organ transplants? The concept of the book is a worrying pit of questions without answers, but it's a future we're rapidly moving towards.