夜歩く (Yoru aruku, Sleepwalker 1949) is the third KINDAICHI Kousuke (金田一耕助) novel by YOKOMIZO Seishi (横溝正史). It's a lot less famous than either Gokumontou or The Village of Eight Graves, which it comes between.
The book is narrated in the first person, like in The Village of Eight Graves; but this time the narrator comes across more as an outside observer. He's an unsuccessful detective story writer, which provides the opportunity for a lot of metaliterary observations on the conventions of detective stories. In this respect, the book recalls the first Kindaichi novel, The Honjin Murder Case and also the long short story 黒猫亭事件 ("The Black Cat Café Case" 1947), which is published in the same volume. As I said in my discussion of the book, the most interesting thing in "The Black Cat Café Case" is probably the discussion of the genre convention of the disfigured corpse; and the ideas expressed there could be taken to be a warm up for this book, which takes the concept to the point of absurdity.
The book is much more concentrated than the longer Kindaichi novels; and the shape of the story as it's presented to us is more like a John Dickson Carr book, except for the absence of a locked room. There is something like an impossible crime, though; but it's deliberately left a little loose round the edges. The narrator's friend tells him that he fears his father might drunkenly attack someone with the Japanese sword in the house. His father has this habit when drunk. The narrator's first sight on reaching the house is of the father pursuing a guest, sword in hand. The sword is said to have been made by Muramasa, a legendary sword maker, whose weapons were said to thirst for blood; and the thought plays on their minds. For some reason the friend wants the narrator's help so that even he cannot get at the sword alone. He locks the sword in the house safe with the key and lets the narrator set the code, so that both of them are needed to open the safe. But in the night they see the daughter of the house sleepwalking from the pavilion in the grounds. Investigating later, they find a decapitated victim there; and when they open the safe the sword is still there, but now covered in blood.
The victim is a hunchbacked man, with a bullet wound in his leg. Normally that would be enough to identify him; but there were two hunchbacked men staying in the house that night. Which is really the victim? And did one kill the other or was someone else the killer? This is the start of a series of games with identity, which continues through further murders.
As a puzzle, on the one hand I have to agree with those who say that it is not really fair play. Still, it's too late for me to join the mob of torch and pitchfork carrying readers that doubtless assembled outside Yokomizo's house when the book was first published. Nowadays, it might be celebrated for overturning the forms of the detective story; and I must admit I am half appalled, half admiring. I can imagine Yokomizo laughing to himself at the thought of readers crying out, 'Have you no honour, sir?' Fair play or not, it has one really good trick in it (which in retrospect should have been obvious, because it involves the kind of detail that normally didn't interest Yokomizo). And solving that trick does lead to the solution of the mystery; but the other hurdles only get removed in the last paragraphs before the answer.
The characters and their behaviour are unusually repulsive in this book. Except for Kindaichi and the police, there are no really sympathetic characters. I think I need to give Yokomizo books a rest for a while and read something a little gentler.