Just before dawn, gruesomely skeletal bodies surface on the Han River. More bodies are discovered all over the nation. The cause of death is determined to be a mutated parasite worm that brainwashes its hosts, ultimately making them jump into bodies of water and to their death. Further research indicates that the worms have only a short incubation period and carry a 100% fatality rate, causing mass general panic. As the number of victims rapidly increase, the government sets up an Emergency Response Task Force and puts all infected citizens into quarantine. But gone insane under the influence of the parasite, the infected people penetrate the quarantine area and jump into the water to their death. Meanwhile, pharmaceutical company salesman Jae-hyeok realizes that his family is infected, and becomes desperate to find the cure. In doing so, he uncovers a frightening conspiracy behind the infection.