Inugami Sahei, who built up the wealth of the Inugami Clan, passes away, leaving a will with Furudate, his legal adviser, for his daughters Matsuko, Takeko and Umeko, all of whom have different mothers, and for their sons, as well as for Nonomiya Tamayo, the granddaughter of a person to whom Sahei feels heavily indebted. The will states that all his assets are inherited by Tamayo alone, on the condition that she marries one of the sons of the daughters. Furudate’s assistant learns the content of the will, and seeks advice from Kindaichi Kosuke, a private detective, as he senses the air of unease. Shortly afterwards, murders start to occur one after another in the clan.