An ordinary office worker named Kim Byeong Gook brutally murders his family and hides out in the office. Then the serial murderer starts picking off the employees of his company, his team members, one by one. Lee Mi Rye, an intern at that company, is at the center of the mystery. Detective Jong Hoon hunts for the serial killer. As he retraces his steps, the detective will be the first to uncover a peculiar work environment and unusual coworker relations.