Disclosure: I translated Ayatsuji Yukito's The Decagon House Murders and The Mill House Murders. And yes, The Labyrinth House Murders is on its way!
Tasogare no Sasayaki (1993) or as the cover also says Whispering in the Twilight, is the third and final book in the Whispering series by Ayatsuji Yukito. The idea behind the first book, Hiiro no Sasayaki ("The Scarlet Whispering" 1988) was that Ayatsuji was thinking of fanning out to genres beyond the pure puzzle plot detective of his House series after writing the first three books in that series. The result was a slasher mystery that was greatly influenced by the famous Dario Argento giallo film Suspiria, but with a twist that reminded you that Ayatsuji was of course a mystery foremost. I generally don't read horror novels or watch horror films (sometimes manga) and while Hiiro no Sasayaki was certainly not a pure puzzler like the House books, it was an okay, even if not super remarkable, horror novel, and as both the series and the books are fairly short, I was always planning to read all of them. The books are not directly connected: in Tasogare no Sasayaki for example, we hear Shouji's family is very distantly related to the Munakata family which runs the girls' academy in the first book, but that's the most "connected" these books get in terms of story. What these books do share, are the titular whisperings: the main characters in each of the three books hear "whisperings from the past" as they very slowly start to remember some traumatic event that happened in their past that they have surpressed, first starting with "whispers" of single words, that slowly become phrases and eventually become whole flashbacks, and of course these events are always related to the murders that occur in each book.
Of the three books in the series though, this book feels the most like a conventional mystery story. Perhaps it's because this book is set in a city, rather than the creepy closed community that was the Seishin Girls Academy, or a large forest in a resort town. While the death of Shinichi is officially deemed an accident, the prologue reveals that Shinichi was in fact attacked by the murderer and that Shinichi, in an attempt to defend himself, fell off his balcony, so we know there's an actual murderer roaming around, but why is the killer after Shinichi and his other friends? Some clues, like an old coin left at the crime scene and the weird phrases mentioned on the phone serve as the only clue, as well as Shouji's vague memories of something that occured that ties the coin and those phrases with Shinichi and his friends.
That does make this book, if you want to read it solely as a detective novel, very... passive. While Urabe and Shouji try to learn more from Shinichi's childhood friends, they remain silent, so a lot of the book basically depends on Shouji slowly remembering what happened when they were young. A lot of their detecting work is really only necessary because Shouji can't remember exactly what happened, even though he knows he was there. His "whisperings from the past" start out as very vague images, and slowly become cleare. This wouldn't be a horror novel if his memories didn't start to return properly only at the very end of the book, but that's a story-telling technique that is probably easier to accept in a horror novel (because the horror is derived from the fact Shouji can't remember yet), but in a detective novel, this device feels cheap because Shouji is holding vital clues but simply can't remember because of narrative reasons, rather than them not being able to interpret clues or make correct deductions.
As an entry in a horror series though, the focus this time is less pronounced on that aspect, which is why it does feel more like a normal detective novel: the death scenes are not as graphic and horrible like in the first book, nor do you have things like the super creepy twins trope (technically, they weren't twins) of the second book, It's basically just a murderer going around killing people in a city, and Urabe and Shouji trying to figure out why and who. Like in the previous two books however, there is a 'big' twist near the end that makes you realize you had been looking
at the facts in the wrong way and that the truth had been staring you
in the face all that time: I absolutely love the big one in this book: it is a bit silly, but it works in this book (especially with the plot device of Shouji only having vague memories at first and the whisperings from the past), and it is surprisingly well hinted at, while also providing great misdirection at the same time. It is a twist that would fly just as well in a proper puzzle plot mystery, which is probably why I think Tasogare no Sasayaki is the most detective-y of the three books. The way events then unfold after this twist is a bit hasty and clearly done in a more horror-storytelling mode than a detective-mode, but on the whole it was a fun read. Like the previous two books, this book is also directly inspired by a horror film, though Ayatsuji refrains from mentioning the film explicitly in the afterword of this book, because apparently it would spoil the twist of the book itself, and it's a "if you know, you know" film.
The Whispering novels are definitely closer to horror-thriller novels than the puzzle plot mysteries of Ayatsuji's own House series, and Tasogare no Sasayaki is no exception to that. While it is closer to a conventional detective novel, it is still very much rooted in the thriller mode, even if it has a fun, surprising twist at the end that would've fitted perfectly in any mystery novel. Overall, I don't think the Whispering series is a must-read, but they are very easy to read and quite short, so I have found them fun to read as a palate cleanser between the more traditional mystery novels I usually read. The first book, Hiiro no Sasayaki is probably the "tropiest" of the three, but I think I liked it the best as a slasher mystery, while Tasogare no Sasayaki is probably the best mystery-thriller of the trio.