Once a free fish in the ocean, the 'Mackerel' was caught by the fishing net and brought to the fish tank in a seafood restaurant. She searches for a way out intentionally and relentlessly since she came into the tank. The skeptic pessimist 'Old-flatfish', was also from the ocean unlike other fishes in the tank raised in the fish farm. As the longest survivor in the tank, he reigns over other fishes with his knowledge of survival. To him, Mackerel's protest against him to escape from the tank is a threat to his regime.