Heiji and Kazuha arrive at the Mori Detective agency revealing he was hired by a man named Shinichi Inubushi, one of the eight illegitimate children of the rich Tsunechika Inubushi. After Tsunechika's death, the health of his wife, Satomi, begins to fail and subsequently two of the illegitimate children are murdered. Believing the murderer is after the inheritance, Shinichi surrenders his share and takes up his mother's surname, Kudo, and has Heiji investigate the murders.