After parting ways with her troubled mermaid tribe, Luce just wants to live peacefully on her own. But her tranquility doesn't last long: she receives news that the tribe is on the verge of collapse and desperately needs her leadership. The tribe's cruel queen wants Luce dead. Dorian, the boy Luce broke mermaid law to save, is determined to make her pay for her part in the murder of his family. And while the mermaids cling to the idea that humans never suspect their existence, there are suddenly ominous signs to the contrary.
But when Luce and Dorian meet, they start to wonder if love can overpower the hatred they know they should feel for each other. Can Luce fulfill her rightful role as queen of the mermaids without sacrificing her forbidden romance with Dorian?