The story takes place after the end of Trace 1 and revolves around Han Sihyun, an investigator of the National Investigation Service (NIS). In attempt to find a way to coexist with "Troubles" instead of killing them, Sihyun frequently proposal to the board of NIS to approve a research on communicating with "Trouble." But after getting his proposal rejected yet again, Sihyun accidentally captured "Trouble" while he was drunk and decided to illegally experiment on it. Though communication seems impossible at first, Sihyun and his "Trouble" slowly begin to close the distant between them and form a bond together.