Masaya is a university student, but he attends a school that's not his ideal school. His days are generally gloomy. One day, he receives a letter from serial killer Haimura. He was convicted for nine murders and received the death penalty. Back when Haimura was committing his murders, he ran a bakery store. At that time, Masaya was a middle-school student and a customer at his bakery store. According to the letter, Haimura confesses to having committed eight murders, but he insists that he did not commit the last murder. Masaya begins to investigate the last murder case involving Haimura.

Lesson in Murder

7 years ago, Yoichi died in a traffic accident. His wife Ryoko did not receive compensation from her husband's death. She has since raised her son Junpei by herself. Junpei is now a middle school student. Ryoko also cares for her father-in-law, who lives in a nursing home and she also runs a cafe. Her care is in a difficult situation due to Covid-19, while Junpei experiences bullying at school.