Yes, this is an awesome cover.
Shimada made his debut in 1981 with Senseijutsu Satsujin Jiken (AKA The Tokyo Zodiac Murders), which also introduced the world to his astrologist-turned-detective Mitarai Kiyoshi and his chronicler Ishioka. Kurayamizaka no Hitokui no Ki is the fourth novel in the series following Naname Yashiki no Hanzai (AKA Murder in the Crooked House) and Ihou no Kishi. This novel also marked a shift in tone, though the previous one already started that, though less ambitious. Kurayamizaka no Hitokui no Ki shares a lot with the novels that followed it: like books like Suishou no Pyramid, Atopos and Nejishiki Zazetsuki, this book is quite long (a so-called brick book) and it features Mitarai involved in a bigger adventure, even going abroad for some time to do some extra investigation. Also, these books take on a a different storytelling style, incorporating more themes like horror, and narratives-within-narratives where Shimada delves into topics that happen to be interesting him at the time of writing. These books are quite different from the two Mitarai Kiyoshi novels currently available in English, but are actually more "typical" of the series than those two, as Shimada stuck to this mode for much longer.
Because I don't really read these books in order, I already knew Shimada would eventually shift to this style, and in a way, Kurayamizaka no Hitokui no Ki is very predictable because of that. Structure-wise, it is quite familiar in the sense I knew we'd be sidetracking a lot while Mitarai and Ishioka are investigating the death of Suguru on the roof. Initially, the mystery revolves around how Suguru ended up on the roof in the first place, whether it was by his own choice or whether someone else arranged for that. Strangely enough, the reason why the two got involved in this case is quickly forgotten and ignored, but as they investigate the case, the reader is also taken along a trip in history, as Mitarai starts to develop an interest in the history of the school that used to stand at this place, and in the family history of the Fujinamis and their father James Payne. In the meanwhile, more mysterious deaths occur, which are clearly centred around the ominous tree standing near the Fujinami parental house and people start to fear it's really a curse that's doing all of this.
Personally, I am not really a fan of the slower pace of the Shimada bricks, where Mitarai obviously has some idea of what is going on already, but he wants to delve deeper in the topic, and thus we get narratives-within-narratives detailing creepy histories or other stories. Some might appreciate the creepy atmosphere of the novel, and especially of the tree, better than I did, but I found the story to be slower than it needed to be, which after a while starts to become tiring. Ultimately, there are few "clear" mysteries that occur (like a death) even though this is a long book, and I didn't think the vague "but something feels off..." atmosphere the book was going for was strong enough to keep the plot engaging enough for the page count.
It didn't help my reading experience that even though there are few 'clear/focal' mysteries in the story, the solution to the mysterious deaths isn't... really surprising. Most of them can be seen as a variant on ideas Shimada uses quite often in his work, and therefore can be easily guessed if you have read a few works by him. This book was hardly surprising seen in a Shimada context in that regard. Of course, I don't read his work in order, so that may have "reverse-spoiled" me, but even so, I do feel the solution to the mysteries is a bit weak considering the length of the book, I would have wanted something a bit more intricately planned. While I guess there's also the bigger mystery of how all the incidents are connected to each other, including those that happened in the past like the dead girl found in the tree long ago and even smaller incidents that happened at the school decades ago, I felt that the merits of this narrative were more in its horror-esque implications, rather than as a detective story. Again, I know that is what Shimada was moving towards starting with this book, but his mode of trying to tie a lot of incidents taken place across a long period of time often ends up feeling rather forced and reliant on coincidences, and while the story can feel quite tenseful, it sometimes has trouble feeling like a proper logical puzzle, being more focused on the "feeling" of the mystery rather than the explanation.
There is a short part that is set abroad, which has its own mini puzzle revolving an odd building: I liked the idea behind that mystery, but it felt really detached from the rest of the book, and I would have perhaps liked it better if it had been its own story, instead of a kind of narrative-within-a-narrative.
Kurayamizaka no Hitokui no Ki was thus not really my favorite Mitarai novel. I do think there will be readers who can appreciate this book better than I, as there are distinct horror elements to the story that will perhaps appeal better to others than to me, and when seen as a series work, this book is also important as it marked the shift to a different story style and it also introduces a certain recurring character who you'll often in other books, so some might want to read this in order exactly so they don't get spoiled on who will survive this book to return in subsequent works, but I personally wasn't too big a fan of this one.