A crime novel involving two sorts of poison: the actual kind, and the toxic malignity of the human heart. In mid-September an old man out taking a walk dies after drinking a carton of tea laced with potassium cyanide. He is the fourth victim since March in a string of such murders. An investigation is launched. We then meet Saburo Sugimura, who works for a prestigious Japanese conglomerate producing its in-house newsletter. When Izumi Genda, his temp assistant, provokes an incident, he calls on an elderly private investigator to look into her background. There he encounters Michika, a high-school student who recently lost her grandfather in a random poisoning. The police, Sugimura learns, are investigating her mother as a possible suspect. Sugimura teams up with Michika to do some amateur sleuthing and find out the truth. Around the same time he discovers that Genda, his colleague, is a pathological liar who misrepresented her age. Her vicious behavior goes from bad to worse. When she laces the water cooler in the department with large quantities of a soporific drug, the police go after her.
Married to the illegitimate child of the company chairman, Sugimura has a five-year-old daughter. Aware that he lacks the ruthlessness necessary for business success, he leads a steady and fulfilling life despite having been excluded from management at the firm. Through his eyes, we delve deep into the psychology of those who spread poison. Though technically a sequel to the 2003 Dare ka (Somebody), the book stands as a complete narrative in itself.