An Ainu sealskin garment that once belonged to Asirpa's great aunt ends up in the possession of Eddie Dun, an American artifact collector. To recover the garment, Asirpa, Saichi Sugimoto, Shiraishi, and Kiroranke must kill the monster that is attacking Eddie's horses. While Asirpa, Sugimoto, and one of Eddie's men learn the truth about the monster, Shiraishi and Kiroranke run into a mysterious duo connected to a crime that took place at the Naganuma Racetrack.