Tempest Maguire is content with her decision to embrace her mermaid heritage and live among her mother's clan within the ocean's depths. Even though training to one day ascend the throne for the aging mermaid queen is rigorous, she finds refuge in the arms of Kona, the selkie who helped her to find her power. But when word comes that one of her brothers has been gravely injured on land, Tempest immediately rushes to his side-which also brings her back to her old flame, Mark. As a dangerous war erupts in her absence at the hands of her old nemesis, the sea witch Tiamat, Tempest's two loves-Kona and Mark, sea and land-will collide for the first time, forcing her to once again choose between her heart and destiny.