Former elementary school teacher and detective, Kurasawa Itsuki (Nakatani Miki), has a history with Kishi Ruoto (Kikuchi Fuma). At the age of 12 and her 6th grade student, Kishi murdered Kurasawa's daughter. The young age of the murderer caused the bizarre murder case to send shockwaves throughout Japan. Kurasawa experienced despair and quit her job as a teacher to become a detective with the desire of "saving as many people as possible from suffering like I did".

Driven by her strong conviction, Kurasawa spends 12 years working hard to solve cases before learning that Kishi is to be discharged from a medical reformatory just before the anniversary of her daughter's death. One day, she receives a text message from the supposedly "completely rehabilitated" Kishi promising to "take away your precious things once again". This was the beginning of a new incident that would shock all of Japan again.