The Han River runs through the heart of Seoul. When the US military dumps toxic chemicals in the river, a monstrous mutant creature is conceived in its waters. The creature reveals itself and wreaks a path of destruction. Gang-du operates a snack bar on the riverbank and witnesses his only daughter, Hyun-seo being taken away by the creature. The sudden and shocking appearance of the mutant creature renders the government and state powerless to act. The once-ordinary citizen, Gang-du, and his family are thrust into a battle with the monster in a desperate attempt to rescue Hyun-seo.