I couldn't decide whether to give this 3 or 4 stars but in the end I'm giving it a 3.5 (kind of in the middle score). The past part of the book was the ending when Cady finds out what really happened during her 15th summer on the island. I was totally surprised the author went in that direction but it definitely gives the story a unique twist. 
 Also, I liked Cady but I don't think I would be friends with her. Did not like Gat and Johnny and Mirren were okay I guess too. 
 I think teens will like this because of the mystery aspect of it and that it is a quick read. 
 I did enjoy the audiobook aspect of it, glad I decided to listen to it instead of reading it.