Kaoru Kanou, a corporate president who is under suspicion for arrest, holds a ballroom event. Among the invitees are Shinjūrō Yūki, a curious detective, his strange assistant, Inga, and Rie, the daughter of police detective Rinkako Kaishō. During the event, Kanou is mysteriously murdered by a knife in his back, with suspicions placed on a member of the SP police who was found shot dead in the hallway. However, thanks to Shinjūrō's detective work, along with the strange abilities of Inga, who transforms into an adult capable a forcing an answer to any one question she asks someone, they soon discover the culprit is Kanou's wife, who wanted him to die a hero.

At the unveiling of a statue created in memory of three youths who sacrificed themselves to dispose of a bomb, two people who were snuck in to try and unveil a purported scam behind the story are found murdered inside the statue. Shinjuurou initially suspects the statue's commissioner, Hakuro Shimada, as the murderer, but Inga's question proves his innocence. After a brief depression and a pep talk from Kazamori, Shinjuurou deduces the culprit to be the statue's creator, Youko, who killed the men before they were transported, before later revealing the location of gold bricks that Hakuro had hidden.

Shinjuurou, along with Rie, Izumi and some others, receive strange invitations supposedly sent by Rinroku. They are brought together at a table where they are presented with weapons, Shinjuurou believes that the imposter Rinroku was the one who appeared at Rie's home, deducing that the Diet member and Rinroku's bodyguard caused the explosion. It is at this point that Rinroku himself seemingly appears with Inga, only for Shinjuurou to deduce that he is actually Izumi's assistant, Shingen Hayami, using Bettenou's power, with the real Rinroku having disguised himself amongst the attendees, having previously faked his death. After a fierce battle, Inga defeats Bettenou and devours her. After the incident, Shinjuurou explains his relationship with Inga to Rie.