When the mermaid performers at Oceanica Marine Park turn violent and attack their handlers, it's Finn Jarvis' job to euthanize them. The work is dangerous, and he botches his latest assignment, causing the death of two additional-and expensive-Mer. His dream of becoming a superstar trainer seems lost until a newly-caught mermaid offers him the opportunity to prove himself.

Erie isn't just any mermaid, she's an ocean-princess that's been ripped from her home. She doesn't know what the landfolk want from her, but she's determined to learn air-words and find out. Alone and voiceless, she watches as the other merfolk are broken into submission, but Erie refuses to be subjugated. To avoid the fate of Oceanica's other Mer and eventually make it home, she needs to make the crowds love her as something more than entertainment.

While Finn trains Erie in her routine, she teaches herself English. Finn has always seen the Mer as ruthless aquatic predators, but Erie seems more human than fish. Soon he finds himself breaking the number one rule at Oceanica: "Never humanize the Mer." Finn's awe-inspiring routine breaks too many rules, and he's soon fired, with a new trainer taking over Erie's show. One that will do whatever it takes to break and silence her.

Finn needs to free Erie before she's broken or killed by her new trainer... or snaps and kills the new trainer herself.

To do that, he'll have to launch a campaign to take down one of the most popular attractions in the world, turn his back on his closest friends and family, and protect Erie from ever being captured again.