In a future where humanity’s neglect of the environment has caused the oceans to rise and flood the continents, only a handful of islands remain above sea level. One of those is the city‑island where Elfie and her grandfather live. During an underwater incident, Elfie discovers she can breathe beneath the waves. Her grandfather then reveals that she is actually a member of the mythical sea‑people. Politicians in the city exploit the residents’ xenophobia, provoking a conflict with the hidden people to divert attention from the region’s resource crisis, and Elfie finds herself caught in the middle.