Okay let me start out by saying that I love Ally Condie and her writing. She has a way of grabbing you and pulling you into the world and keeping you there until you can't turn the pages anymore because the book is done. Atlantia is an underwater city created after the "Divide" when air pollution above ground became so deadly that people couldn"t survive for a long time. Civilisation was divided into two areas - the Above and the Below. Families were separated so that those Above would have incentive to continue working in order to send supplies (such as food) Below so that they could survive. Centuries later is when Rio"s story takes place. The story begins on the anniversary of the Divide where children of a certain age choose whether to continue living Below or move to the world Above. This was very similar to the choosing ceremony in the Divergent series. Even down to there being bowls in front of the minister representing the Below (water) and the Above (dirt). Similarly, the families of those choosing to go Above didn"t know about their intentions. This includes Rio"s sister, Bay, who has made Rio promise not to go Above herself despite this always being her dream. Their mother (who was previously the minister) was murdered and Bay made Rio promise that she wouldn"t leave her alone. I was taken at betrayal and underworld so when I started reading and found out what one twin did to the other and how the parents were dead I knew I was going to go on one hell of a journey and journey is what I got.Can you imagine living with your twin and doing everything together and one day your twin decides she is going to leave you? Man that is what happened to Rio. In this story it flows so smoothly that as I was reading I could hear the artificial air breathing in and out and thinking about what a sirens voice sounds like. See because one of the twins is gifted with a gift so rare that she shares it with no one but her sister. Then when things go wrong one of the sisters will go on the hunt for the truth and what she finds out is more mystery and intrigue. This is a great story and a must read!