With the development of a new electromagnetic induced train system, the old subway has lost it's credibility, becoming a seedy haven for prostitution and drug-dealings called "Paradise Loop". Recently, a string of murders have broke out in this area. The victims, all prostitutes, are found with their abdomens slashed open by some sharp instrument in the same manner. Why does the murderer only chose prostitutes? Can this hideous crime be committed by a human being? Or is a Boomer responsible for the killings? Soon, the investigation leads to a woman who seemingly has no connection to the crime whatsoever...