Rio Conwy has always dreamed of leaving Atlantia and living Above. However, during the ceremony where twins must choose their future, her sister Bay unexpectedly leaves for the surface, forcing Rio to stay behind. Confused and heartbroken, Rio begins searching for answers and uncovers secrets about her family's past, her mother's death, and her own hidden power as a siren. With the help of a boy named True and her mysterious aunt Maire, Rio must discover the truth and find the courage to save both her sister and her city