In an alternate universe where mermaids are critically endangered animals, a team of marine biologists off the coast of Jeju Island embark on a decade-long journey to revive the over-hunted, largely-infertile species. The researchers' hopes are set on one dominant female, but when their tampering crosses an irreversible line, their mission— and her life— become jeopardized. In an alternate world where mermaids are real and critically endangered, a team of marine biologists near Jeju Island embark on a decade-long mission to revive the over-hunted and overwhelmingly male species. The scientists set their hopes on one dominant female and her two male companions. However, as they study their sexual lives, the team learns just how complicated an "animal" can be— and how, sometimes, conserving a species comes at the cost of some of its members.