Although anime and manga fans are more likely to know him as the author behind the horror story Another, The Decagon House Murders is probably the literary work Yukito Ayatsuji is best known for. First published in Japan in 1987, it didn’t make it into English translation until 2015 and was recently republished by Pushkin’s Vertigo imprint, which specializes in classic mysteries in English translation, including an impressive number of Japanese titles such as Soji Shimada’s The Tokyo Zodiac Murders and Masako Togawa’s The Lady Killer. The Decagon House Murders stands out among the publisher’s offerings for a few reasons, with perhaps the most important being that the book is largely credited with bringing back honkaku mysteries, otherwise known as “fair play” mysteries in English. The hallmark of a fair play mystery is that the reader can solve the crime along with the detective, and they flourished during the Golden Age of mystery fiction, which roughly corresponds to the between-the-wars period. (For a point of reference, Arthur Conan Doyle‘s Sherlock Holmes stories and Edgar Allan Poe’s C. Auguste Dupin stories are not fair play, while in Japan Edogawa Ranpo’s body of work contains both varieties.) The other notable feature is that Ayatsuji’s work is part of a body of novels that uses Agatha Christie‘s 1939 locked room novel And Then There Were None as its influence – and it wears that as a badge of pride.
The story takes place in the late 1980s and follows a group of university students from K University’s Mystery Club, something like a literary club that focuses exclusively on mysteries. As part of their gimmick, many members take for nicknames the names of famous foreign mystery writers, with the seven the story primarily revolves around going by Ellery, Van Dine, Agatha, Orczy, Poe, Carr, and Leroux. Interestingly enough, several of these authors have fallen off the public radar or are known for their non-mystery work for English-speaking audiences; Baroness Orczy is more typically associated with her French Revolution-era spy novel The Scarlet Pimpernel, for example. The club members are all proud of their aliases, but perhaps none more so than Ellery, possibly because his name is both the pseudonym shared by two cousins and the name of the detective they wrote about, putting him closer to the role of “great detective,” at least in his own mind. It’s also significant that S. S. Van Dine is among the nicknames, because Van Dine is today largely associated with the set of twenty rules that all “good” mysteries must follow – rules that Ayatsuji is ostensibly taking into account as he tells the story. (Van Dine is also a pseudonym for Willard Huntingdon Wright, which may be worth remembering as well.)
In a stated homage to Christie’s novel, the seven students are headed to a relatively remote island off the Japanese coast to stay in an abandoned building there. Six months prior to the story’s opening, the owner and builder of the house died when the adjacent mansion burned to the ground, and since the body of one of the five people who were on the island at the time was never accounted for, the case is considered unsolved. Since Van Dine’s uncle bought the island after the heir didn’t want it, he’s arranged for the seven club members to spend a week there. They don’t have much of a stated goal beyond basically murder tourism, and, like in Christie’s book, they tell the fisherman who drops them off not to return before their week is up. Shortly after their arrival, however, a set of plates labeled “The First Victim” through “The Final Victim,” “The Detective,” and “The Murderer” appear on the table of the odd decagonal house. This, the students quickly realize, is analogous to the “Ten Little Soldier Boys” poem in Christie’s work, and like in And Then There Were None, the appearance of the plates kicks off a series of mysterious murders.
The novel divides its pages between what’s happening out on the island and what’s going on with two of the club members and an amateur detective on the mainland. One of the club members, who was known as Conan Doyle before he quit the club, is horrified to one day receive a letter in the mail from Nakamura Seiji, the man who built the houses on the island. In the letter, Nakamura accuses the members of the club of having murdered Nakamura Chiori, his college-age daughter, who was in the club at the time of her death, dying of alcohol poisoning at a club event. Since Seiji was believed to have died on the island, this raises the question of who, exactly, the missing body was six months ago; perhaps it was not the gardener as the police assumed. This speculation comes to the mind of Ellery as well, and the students on the island begin operating with the assumption that Nakamura Seiji is in fact alive and is now picking off the students for his own reasons. (None of them are aware of the letters, having left before they arrived.) We thus see the mystery more fully than any of the characters in the novel, being privy to both Conan Doyle’s discoveries with the amateur detective and Ellery’s theories on the island, as well as the actual deaths.
This does make it a true fair play mystery, although some of the clues are fairly obscure. Knowing the origins of everyone’s nicknames factors into it to a degree, as does familiarity with And Then There Were None: many plot elements are nods to the solutions and mysteries in Christie’s book, such as the order of the deaths, the occupations (majors) of the people on the island, and the theories that the people on Soldier Island come up with to explain what was happening in 1939. Interestingly, it is a nod to Christie that ultimately stops the murderer from getting away with it, which is a particularly nice twist on the original, where the murderer had no illusions about what they were doing. Ayatsuji seems to be having a lot of fun playing with the elements of Christie’s novel, and while it isn’t strictly necessary to have read it, you will get more out of this book if you have. (Or have seen the 2015 mini-series version, which hews very close to the source.)
The Decagon House Murders feels like exactly what it is: an homage to Agatha Christie, Ellery Queen, and the other greats of the Golden Age and the fair play mystery seen through the eyes of the author who would go on to write Another. It isn’t perfect and does enjoy its own schtick a bit much at times, but it’s also a lovingly crafted ten-sided puzzle box with a different author on each face. It’s a good example of both the genre and Ayatsuji’s work, and whether you’re a mystery buff or just like to read the source before reading the adaptation (Kodansha is releasing the manga version in English), this is worth your time.