The episode begins with the young detective Isshiki Totomaru, who is frustrated because he cannot solve a series of serial murders. His colleague Kiku suggests that he consult Ron Kamonohashi, a former detective who has withdrawn from the world.

Totomaru visits Kamonohashi's apartment, which is full of cushions and lacks any modern technology. Kamonohashi initially refuses to help him, as he has a "fatal flaw" that prevents him from being a detective. However, upon hearing about the sixth victim, Kamonohashi agrees and warns Totomaru to keep an eye on him.

The duo heads to the crime scene in Kazahana Park in Shibuya, where Kamonohashi quickly deduces the cause of death and the modus operandi. He identifies the murderer as a hairdresser who knocks out his victims with oxygen-deprived air and then drowns them. Kamonohashi and Totomaru go undercover and visit a hair salon that fits the criteria. There, Kamonohashi exposes the hairdresser as the murderer and apprehends him with Totomaru's help.

At the end, Kamonohashi reveals his "fatal weakness": he unconsciously drives the culprit to their death, which explains his 100% resolution rate but 0% arrest rate. Totomaru's intervention breaks this cycle, and Kamonohashi suggests that they become partners. Totomaru agrees, and their mysterious partnership begins.

The episode introduces the main characters and lays the foundation for their future investigations.