Off the coast of Louisiana, on a small island, stands a mysterious stone tower 30 meters tall. The top floor of this tower became the site of the death of a well-known member of America’s richest clan on August 15, 1986. His body was found drowning in seawater, with eyes filled with horror, and in a pose as if he were swimming the crawl. The entrance to the tower was sealed with a massive safe door locked from the inside, and the observers noticed nothing suspicious around the tower. The genius detective Kiyoshi Mitarai is the only one who can unravel this impossible riddle of death.