A woman is found dead after visiting her childhood friend, a director, at the Meijiza theater. The detective in charge of the investigation questions the relationship between this body and a burnt corpse discovered nearby, and finds the names of the 12 bridges surrounding Nihonbashi inscribed on the deceased's possessions. Detective Kaga Kyouichirou is shaken on learning this, for it ties the murders to his own mother's solitary death.