Lily Sanderson has a secret, and it's not that she has a huge crush on gorgeous swimming god Brody Bennett, who makes her heart beat flipper-fast. Unrequited love is hard enough when you're a normal teenage girl, but when you're half human, half mermaid, like Lily, there's no such thing as a simple crush. Lily's mermaid identity is a secret that can't get out, since she's not just any mermaid she's a Thalassinian princess.