By Mr. Ngaihte (27 Apr 2011)
After a careless Morgue empties hundreds of bottles of formaldehyde into the sewers near Seoul's Han River, it gives birth to a terrifying mutant with a taste for blood. The Mutant abducts the daughter of Gang-du (Kang-ho Song). Thinking she is dead, the family mourns her loss; until they receive a late-night call from her cell phone. Knowing she is alive, they band together to find and rescue her from the mutant before it is too late.
Their attempts are thwarted by a paranoid Government, who is claiming that the mutant is "living biological warfare", after a Marine from the United States contracts a mysterious disease from coming in contact with the creature. Fearing another SARS incident, they seal off the area the mutant is known to patrol and quarantine anybody and everybody who has came in contact with the mutant - including Gang-du and his family - though no virus actually exists.
As the U.S Government bears down on South Korea in an attempt to contain the creature and the supposed "virus" it is carrying, Gang-du and his family break free to confront the monster head-on. However, in the midst of all of this, the American Government finally reaches the end of it's rope and carelessly unleashes "Agent Yellow", a dangerous and toxic gas the U.S. Military had been developing to help fight biological warfare. Though the U.S. Government assures it is safe to use, the people of Korea protest its use at the edge of the Han River where "Agent Yellow" will be unleashed - making them an easy target for the mutant.
Gang-du, his family, the mutant, and the government all confront one another in a dangerous battle that ends with both the monster - and Gang-Du's daughter - dead.
In a medical facility, an American Doctor tells his Korean assistant to dump numerous dusty bottle sof formaldehyde into a sink that drains to the Han River. The assistant claims that it is only the bottles that are dusty, but the doctor still wants his request carried out.
A few years later, two men are fishing in the Han River, when one sees a small, strange creature in the water. He manages to catch it in a coffee cup, but upon trying to touch it, the thing bites him. This causes the man to drop the cup, and the creature falls back into the river and disappears.
Four years afterwards, a businessman commits suicide by jumping off a bridge into the Han River, but not before noticing a dark form moving in the waters below him.
The film the cuts to the present day at a snack stand near the Han River. Park Gang-du is lazily running the stand, with his father Hee-Bong trying to get him to behave responsibly. Eventually, Park's daughter Hyun-Seo returns from school. Hyun-Seo is embarassed that her uncle Nam-il arrived for a school event drunk. Hyun-Seo and Hee-Bong then retreat to the snack trailer and watch an archery tournament being broadcast.Hyun-Seo's Aunt Nam-Joo is competing, but due to her taking her time, she ends up winning a Bronze medal.
Meanwhile, Park and some other people on the riverbank have noticed a strange creature hanging underneath a bridge. It then swims over and begins to attack several people along the riverbank. Park and an American serviceman attempt to stop the creature, but end up only harming it before it attempts to attack the two men. Hyun-Seo emerges from the snack stand and is grabbed by the creature's tail before it plunges back into the river.
A makeshift shelter is held in a local center, with photos displayed of the victims. The family membes congregate there, until a group of men in yellow suits evacuates the center, asking if anyone had contact with the creature. When Gang-du explains that he got some black stuff from the creature on him, he is put in a containment suit and whisked off to a hospital with the rest of the family in tow. With no additional word regarding his condition once he's there, the family are forced to remain nearby.
That evening, Gang-du's cellular phone buzzes, and he can hear Hyun-Seo's voice on the other end, saying she's in a pit somewhere. Gang-du relays this to the medical staff the next day, but his description of events on how his daughter can possibly still be alive leaves them thinking he's crazy. However, the rest of the family is willing to believe him. Using an outside contact, Hee-Bong is willing to sacrifice his life's savings to hire a group of men to help the family escape from the hospital. They manage to obtain a truck and some plastic hazmat suits, along with a supposed map of many tunnels and sewer openings that lead in and out of the Han River.