Living under her father's suffocating overprotection, Vivienne, the youngest princess of the mermaid kingdom, feels as if she is drowning despite living underwater. When she finally reaches her rutting season and secretly surfaces, she falls head over heels for the most brilliant male on land. Desperate to reach him, Vivienne strikes a dangerous bargain with a witch: 'When the red moon rises, if you are carrying that male's offspring, you can become a human.' She thought her temporarily acquired legs would allow her to reach him. But one day, after seeing traces of taxidermied mermaids in a suspicious room in his mansion, she realized: she had walked right into a trap.