I was ready to give this a solid 3 stars and then BAM.... the twist.! That bumped it up for me. 

I feel that it is really slow.... until you get to the point of Cady's accident. What really happened and why can't she remember? It's basically rich people on their own little island where all they know are each other for the summer. 

It's interesting what the brain will do in times of trauma. When I got the full story of what happened.... wow. When I say my jaw dropped, it DROPPED!