In 1946, on a fictional island called Gokumon-tou, located in the Inner Sea of Seto, the famous detective Kindaichi intended to pass his convalescence after the invitation of his war buddy Kitou Chimata, the successor son of the powerful clan of the Kitou Family. But Kindaichi arrives alone, bringing the bad news of Chimata's death. However, the truth is that Kindaichi is not on the island to recover. Before Chimata died, she uttered the words: "My sisters will be killed!" Indeed, as the three sisters are murdered one by one in horrible and strange ways, Kindaichi desperately tries to find the culprit and in the process discovers the intrigues of the family, secrets, island mentality, discrimination, and eccentricities, With the backdrop of the turbulent postwar period.