Itsuki Kurasawa was once an elementary school teacher, but she now works as a detective. When Itsuki was a teacher, her daughter was brutally murdered by her 12-year-old student Ruoto Kishi. The horrific case shocked the entire nation at that time. Afterwards, Itsuki decided to become a detective to save people in desperate situations like she was in. Twelve years after the murder case, Itsuki is busy solving cases as a detective. She knows that Ruoto is going to be discharged from a medical juvenile training school and she hears that Ruoto is now completely rehabilitated. As a family member of the victim, Itsuki can't help having suspicions about his true nature. One day, Itsuki receives a message that says "I'll take your precious thing once more."