On an earth split in half by an ancient curse, Ali and her team are cast into the centre of Atlantis' rule.
Ali and Yuki are coming to the end of their training and will graduate to become Atlantis guardians. But their second-last mission does not end well. Their captain gets some bad news: his brother Ray, also a captain, is missing. Ali and the rest of the team fly home to their drowned capital, but the news only becomes worse.
Ali is already nervous enough about the graduation, but now Atlantis' power awakes when she comes into contact with the old magic. This is not the only force to waken; dark powers are rising too. Ali is marked, putting herself and the team in danger as the power-hungry group called Descendants of Hades become more than legend. Cracks in their world are beginning to show; trouble could leak into the human half, starting a war with past powers that never really went away.
Time is running out and Ali will need all of her friends and magic to combat this terrible threat.