Todo Hinako is a rookie detective assigned to the #1 investigation team at the Tokyo Metropolitan Police Department. She became a detective because she wants to find the boundary between people who kill and those that do not. One day, Hinako and her colleague detectives go to an area where a body was found. The case is presumed to be a suicide case, but the dead man is a suspect in an unsolved murder case. The man died in the same manner as the victim in the unsolved murder case.