Tanimoto Masahiro, a police officer who works at a police post in a park within the metropolitan area, is found shot to death. His shoulder strap has been ripped off, and his gun and whistle have gone missing. At first, it is not able to determine if it was a murder or a suicide but forensics examiner, Kuraishi Yoshio, concludes that it was a suicide from the circumstances and traces of gunpowder burns. Someone had taken Tanimoto’s gun away after he committed suicide. Tanimoto has no wife and he does not get along well with his only daughter. Furthermore, he is afflicted with cancer, and it is thought that the three-month life expectancy that he had been given, was the reason for his suicide. Before long, the stolen gun is found. It is gripped in the right hand of a person who has died an unnatural death …