After being transformed into a mermaid by the irresistible Carter Stevens, Ava Adair finds herself submerged deep in the sea without the ability to return to land. She trades a beachfront condo with her best friend and future plans to go to college for a life where her sole purpose revolves around Carter and the mermaid traditions she wants nothing to do with.

Fitting in with other mermaids is the last thing Ava wants, and after refusing to go through the coupling ceremony with Carter, Ava falls under the scrutiny of the colony's mighty king, who would wipe out towns to keep his kingdom safe. When the king threatens not only her relationship with Carter but also the chance of reuniting with her family, Ava must figure out how to escape from the ocean and the king's rule or never see the beloved shores of her home again.