When the superpredator Mer kill another trainer, Finnegan Jarvis finally sees his opportunity to become a superstar trainer. No more scrubbing tanks and cleaning blood: he's gonna be in front of the audience showing off his brand-new, fully-trained mermaid. If only he can get her to do the tricks she's supposed to.

That mermaid is Erie, an ocean-princess ripped from her home when she pushes another Mer out of the way of the net. She doesn't understand why she's there, but she's determined to learn air-words to find out.

While Finn trains Erie, she teaches herself air-words. And when she finally speaks, Finn breaks the number one rule at Oceanica: Never Humanize The Mer.

Now he'll do whatever it takes to save her.