Reanna glimpsed the depths of Atlantis, and now she must survive the consequences.

After Reanna's ill-fated attempt to stop Atlantis' war, the Council of Solis holds her life and the lives of her friends in their hands.

But amidst this turbulence, the legendary mermaid Thessalonike reappears with a guardianship offer. She takes Reanna and Co. to her underwater library, but her training is not what they expect. Nor is her end goal, which involves reconstructing the trident of Atlantis with the help of Reanna's long-lost cousin Marri and without the Council's sanction.

In the face of Thessalonike's tactics, the ever-growing danger of the war, and the weight of their own dueling desires, Reanna's found family must decide whether they will pull together, or if the twisted tides will rip them apart.