Storyline

On 09 February 2000, the American military base of Yongson releases toxic chemicals in the drain to the Han River under the direct order of an arrogant coroner. Six years later, a mutant squid monster leaves the water and attacks people on the side of the river. The teenager Park Hyun-seo is carried by the creature and vanishes in the river. While grieving her loss, her slow father Park Gang-du; her grandfather and owner of a bar-kiosk nearby the river Park Hie-bong; her aunt and archery medalist Park Nam-Joo; and her graduated unemployed uncle Park Nam-il are sent by the army with all the people that had some sort of contact with the monster to quarantine in a facility. During the night, Gang-du receives a phone call from Hyun-seo telling that she is alive in a big sewage nearby the river. Gang-du tell the militaries but nobody believes on his words, saying that he is delusional due to the shock of his loss. The Park family joins forces trying to find Hyun-seo and rescue her.