Suspect

Yasuko Hanaoka is depicted as a divorced, single mother who owns a restaurant, living a relatively quiet life with her teenage daughter Misato. Her daily routine includes exchanging greetings with her reclusive neighbor, Tetsuya Ishigami, a brilliant mathematics teacher. Their interactions are described as the brightest part of Ishigami's day, establishing his solitary nature.

Togashi, Yasuko's abusive ex-husband, appears unexpectedly at night, demanding money and threatening Yasuko and Misato. The situation escalates with violence, leading Yasuko and her daughter to defend themselves. In a desperate act, Yasuko and Misato kill Togashi to prevent further harm, resulting in a murder in their apartment.

Overhearing the commotion from his room, Ishigami deduces that Togashi has been murdered. He offers assistance to Yasuko and Misato, revealing his intelligence and calm demeanor. Recognizing the severity of the situation, he agrees to help them cover up the crime.

Ishigami helps Yasuko and Misato carefully dispose of Togashi's body, carefully planning each step to avoid suspicion. His methodical approach demonstrates his analytical skills and determination to protect the mother and daughter. The disposal marks a turning point in their attempt to conceal the murder.

Togashi's body is found and identified, leading to suspicion falling on Yasuko and her daughter. The police become involved, complicating the case with the potential for evidence to reveal their involvement. Detective Utsumi and her team begin their investigation, seeking answers.

Detective Kusanagi and Utsumi seek the expertise of Professor Manabu Yukawa, a renowned physicist, to help with the case. Initially reluctant because the murder appears straightforward, Yukawa's curiosity is piqued when he learns that Ishigami is his former classmate and neighbor, leading him to investigate further.

Yukawa visits Ishigami, rekindling their friendship and starting his own investigation into the murder. Both men engage in a battle of wits, with Ishigami doing his best to outthink Yukawa and protect Yasuko, employing his logical skills to mask their involvement.

As the investigation progresses, Yukawa analyzes the case from a scientific perspective, examining alibis and evidence to find inconsistencies. His deductions lead him closer to understanding the truth behind the murder and the clever cover-up orchestrated by Ishigami.

Yukawa finally uncovers the shocking truth behind the murder, revealing an outcome that is tragic and heartbreaking for all involved. His success in solving the case exposes the complexities of justice, morality, and human nature, leading to an emotional conclusion.

Despite his reputation for detachment, Yukawa is visibly distraught by the case's outcome. His emotional response underscores the moral dilemmas faced during the investigation, highlighting the tragic consequences of the choices made by Yasuko, Misato, and Ishigami.