After scientists at a US base in Seoul have emptied expired chemicals into the drain, a mutation of a huge amphibious monster occurs. On a sunny day, the beast rises from the river and devours passers-by one by one. Gang-du flees with his daughter, but she is caught by the beast after a confrontation. Everyone thinks she is dead, until Gang-du gets a call from his daughter, who seems to be trapped in a canal system. He does everything in his power to save her.