In a dystopian Korean society, a wall segregates Omegas—mutated humans with fins—from regular humans. Omegas are exploited to clean oceans under harsh conditions. One Omega escapes to fulfill his dying father’s wish: deliver his fin to the daughter, Mia, who lives disguised among humans. Mia works in a fishing nostalgia shop until a government worker, Sujin, plagued by anti-Omega sentiment, becomes suspicious of her identity