After a biological terrorist attack kills off the population of a Russian town; Japan's Public Safety Special Third unit, code name THIRD-i, believes that the terrorist organization responsible plans to unleash the same virus known as Bloody X into Tokyo. Subsequently, THIRD-i recruits the help of genius hacker Takagi Fujimaru to find out what happened in the Russia. However, as Fujimaru becomes involved, he soon finds out that he is in over his head and that the terrorist groups influence reaches not only his school but even the police. Fujimaru must now rely on his skill as a hacker to unravel the organizations sinister plot and find out the truth behind "Bloody Monday."