Teenage mermaid Danika DelMar loves high school more than anything in the ocean. She fights with her mother about joining their pod, but she fights her hormones even more. No matter what her body says, she's not ready to kill someone with sex. Things get harder when Danika falls for a new boy at school. He claims to be a sea creature like she is, but she isn’t sure she can trust him or herself.

When a dead body shows up at Danika's reef she risks giving away her secret to make sure the police find the victim. It doesn't stop the bodies from coming. Soon she's lost her friend and the first boy she ever loved. Danika is sure a sea creature is involved, and she’s the only one who can help. As her friends become targets, Danika races to find the killer.