Atlantia by Ally Condie

   

 A fast-paced fantasy adventure tale in a richly drawn dystopian future. Despite her lifelong dream of living Above, recently orphaned Rio has promised her twin sister, Bay, that she'll stay in their underwater city of Atlantia when they come of age. In one shocking moment, however, Bay is headed Above, and Rio is left alone.  As Rio tries to find her own way to get Above, she also discovers pieces of Atlantia's hidden past and its uncertain future. Ultimately, the protagonist will have to rethink everything she's been taught and make courageous decisions on her own in order to reunite with her sister and save the world she loves. .Review Source:  School Library Journal