This film is adapted from the masterpiece of Ayatsuji Yukito, the first modern orthodox mystery writer. It tells the story of the unlikely encounter between the pair of Konan and Shimada, who received a "letter from the dead" in the "homeland" of Tsunoshima, far away from the "Jukakukan" with a peculiar decagonal appearance. The genius architect who died half a year ago... begins to investigate the truth behind Nakamura Aoji's death and unravel the shocking truth hidden in the murder case that occurred in the "Jukakukan".