A landmark Japanese mystery novel by Yukito Ayatsuji that revitalized the classic "fair-play" detective story and launched the influential Shin Honkaku (New Orthodox) mystery movement in Japan.

The story follows seven university students, all members of a mystery club, who travel to the isolated Tsunojima Island. Their destination is the eerie Decagon House, a uniquely designed mansion built by a mysterious architect. Each student adopts the name of a famous mystery writer, adding to the novel's homage to classic detective fiction.

Soon after their arrival, members of the group begin dying one by one under seemingly impossible circumstances. Meanwhile, on the mainland, another mysterious figure starts sending disturbing letters that hint at a dark secret connected to a murder that occurred on the island months earlier. As the two storylines gradually converge, the truth behind the killings is revealed in a brilliantly constructed finale.

Inspired by the works of Agatha Christie, especially And Then There Were None, The Decagon House Murders is celebrated for its ingenious plotting, fair-play clues, and unforgettable twist ending.