“A completely undetectable poison that kills 24 hours after consumed.” It is the rumour that has spread on the internet of a lethal drug that makes the perfect crime possible. It has even become a topic at the Tokyo Metropolitan Police Department’s Special Crimes Unit which Sasamoto Naomi has been transferred to. The background of Professor Matsui Toichi who invented this poison at an East European university is obscure. What is known of him is a fuzzy picture on the internet and the digits inscribed on the back of his hand. Matsui has disappeared but starts to appear before people who are trapped by their problems and hands them the poison. “You are free to use it as you will,” he would tell them. Meanwhile, magazine journalist Akimoto Shunji who is engaged to Koide Reika, the daughter of the president of his company, learns of this poison too. He has a problem. It is the existence of Otsu Mayumi, a former high school classmate with whom he has been carrying on a relationship for half a year. She poses an obstacle to his marriage to Reika. And so, he attempts to broach a breakup with her, but is told that she is two months pregnant. On the way home, a troubled Akimoto is hailed by Matsui who passes him a small bottle with the poison. Later, Akimoto is invited to a meal at a posh restaurant by Reika’s father and forced to vow marriage to Reika. He puts a drop of the poison in Mayumi’s cup in order to protect his bright future even as he struggles with himself. Mayumi unsuspectingly brings that cup to her lips... On the morning two days after the incident, her dead body is found at an unexpected place. Adapted from 1981 novel "Doku" by Akagawa Jirō.