This review had to be posted after another one I had already written and scheduled, otherwise I might have just pushed this one ahead and posted it the moment I finished writing. But I didn't want to mess up the order scheduled posts too much...
The Kannagi Uromu series was a series of succesful non-fiction books by high school student Mitsurugi Masaru based on the real adventures Masaru had with his childhood friends Kannagi Uromu and Hoshikawa Kaguya. Uromu was an absolutely brilliant detective who managed to solve many seemingly unsolvable crimes. Masaru himself considered himself only an "observer", writing down these adventures, but Kaguya, and their later allies Watarase Suzune and Minamori Izuko proved themselves to be very capable detectives themselves too as they assisted Uromu. Uromu however was a very people-shy person and never appeared in public, which was why Masaru wrote down their adventures as fair-play mystery novels. The Detectives and their Observer had one nemesis whom they would encounter in several of Masaru's accounts: the "King of Phantom Thieves" Kuonji Sharaku, also known as Demon's Gate Syndrome. He and his five Disciples would commit the most baffling and surprising impossible crimes, though they never hurt anyone during their crimes, which only added to the sense of entertainment of these confrontations between the Detectives and the King of Phantom Thieves. This legend of Kannagi Uromu however fell apart soon after the publication of The Last Case of Kannagi Uromu, which was a record of the final confrontation the Detectives had with the King of Phantom Thieves, which started with an invitation by Kuonji Saharaku to the Detectives to his secret hide-out the Musical Box House. At the end of their adventure, both Kuonji and Uromu had disappeared. The Last Case of Kannagi Uromu was an anomaly in the series, as the truth behind the mysterious death that occured in the Musical Box House was not revealed in the book and with Uromu gone, nobody really knew what happened there. But not long after the release of The Last Case of Kannagi Uromu's release, the rumors started: Mitsurugi Masaru was accused of being a fraud and that there never was any Kannagi Uromu. With Uromu being immensely people-shy, he was never seen by outsiders, fueling these beliefs and as online message boards were the main form of social media back then, these rumors quickly spread through BBSes, accusing Mitsurugi of having fabricated all these stories. Mitsurugi and the other Detectives however did not fight back against these rumours, and the publishing world immediately pulled away from these books and from their author Mitsurugi Masaru. The books became out of print and a thing of the past, and Kannagi Uromu would turn into an old internet rumor people would hear about once in a while.
Almost two decades almost later, and Shinonome University students Hakuto and Shiki are walking together on the streets. Not because they're dating, Hakuto assures the reader, even if he would very much like that, but even though they are always hanging out together, take turns cooking every night, he helps her with her studies and they also joined the same club, Hakuto sadly enough has to admit they're, in the end, simply neighbors in the same building. But while walking together, they see a woman collapsing on the street and they bring her back to Shiki's room. The woman was also carrying a book, which turns out to to be The Last Case of Kannagi Uromu. The woman introduces herself as Mitsurugi Yui, a fellow Shinonome University student and the daughter of Mitsurugi Masaru, the man who was accused of being a fraud, and of Hoshikawa Kaguya, one of the Detectives, but her mother left Yui and her father when she was young. She explains that the adventures her father had as a high school student with Uromu, Kaguya and all the other people were real. Yui wants to learn what really happened in the last confrontation between the Detectives and The King of Phantom Thieves, but due to circumstances she can't ask her father (the writer) about it. Yui asks Shiki and Hakuto if they happen to know someone who can help her, and as it happens, they do. As both Shiki and Hakuto are (involuntary) members of the Detective Club, led by Kongouji Kira. Kira hails from a rich family and may seem like a spoiled brat, but she's actually really intelligent too, and has solved many cases. She does act exactly like she owns everything and everyone though, and when Yui asks Kira to find out the truth, Kira decides to order the members of the Detective Club all to come up with a solution to The Last Case of Kannagi Uromu. They are all to read the book, while Kira will use her "special means" to get more information from official sources, and they all have to find out what really happened in the Musical Box House two decades ago. But as each of the members try to come up with a solution to the problem, it's only Shiki who wonders whether Yui should really know the truth, and whether a plausible solution isn't better for her sake. But what answer do the members of the Detective Club arrive at? That's the big question in Konno Tenryuu's Kannagi Uromu Saigo no Jiken ("The Last Case of Kannagi Uromu" 2022).I had previously read Konno Tenryuu's two Alchemist novels, as well as Cinderella-jou no Satsujin ("The Cinderella Castle Murder" 2021), all entertaining mystery novels featuring fantasy elements, so I was quite pleasantly surprised when I noticed his Kannagi Uromu Saigo no Jiken had taken the ninth place in the Honkaku Mystery Best 10 ranking for 2023 (which covers books published late 2021 - late 2022). The book was released in the summer of 2022, and I had been eyeing it for a while, but I hadn't expected it to get picked as one of the best honkaku reads of the year. I was a bit surprised that unlike the other mystery novels I read by Konno this novel didn't use fantasy elements. What surprised me the most however was the dedication found at the beginning of the book. For it was a reference to Spiral ~ Suiri no Kizuna 2: Koutetsu Banchou no Misshitsu ("Spiral ~ The Bonds of Reasoning 2: The Locked Room of the Steel Gang Boss"), a book which had been out of print for almost two decades, but which I happened to have read only two weeks before starting on Kannagi Uromu Saigo no Jiken, so it was a complete coincidence I recognized the reference at once and that I was reading these two books in order! This obviously felt like destiny, so while I originally bought the book and was only planning to look inside to see how long it'd be etc. and then read it later, I decided to move it up the reading list right away.
The common points between the two books are of course very easy to recognize: just like Spiral ~ Suiri no Kizuna 2, Kannagi Uromu Saigo no Jiken is a story where a crime happened in the past, and where a record of this crime (in this case, the novel The Last Case of Kannagi Uromu) is used to come up with an interpretation of what happened so long ago. Both books also revolve around the concepts of multiple solutions, which in this book is done by having Kira command her club members to all come up with a solution themselves for the events in The Last Case of Kannagi Uromu because that's more fun, and there's also the notion that the truth isn't the most important factor in this story, but that there should be a solution that is the best for Yui herself, because the truth might not be what she really wants to know. Kannagi Uromu Saigo no Jiken follows a two-part structure, with the "contemporary" narrative starring Hakuto and Shiki at times interrupted by whole chapters and some excerpts from The Last Case of Kannagi Uromu, which incidentally is clearly written very differently from the contemporary narrative, so it does really feel like a different 'novel-within-a-novel.' Apparently there are quite some readers who first got acquainted with the concept of multiple solutions in a mystery novel through the second Spiral novel, which explains why Konno added that dedication.
The Last Case of Kannagi Uromu, as a novel-within-a-novel is quite interesting to read, as while it's supposed to be a "non-fiction" book about the real adventures Masaru, Uromu and his friends had as a high school student, it reads a lot like a grand Great Detective adventure novel, with mysterious manors, Disciples who serve the King of Phantom Thieves and some characters even carrying named weapons like they were in an RPG. This story has Uromu and his friends invited to the residence of the King of Phantom Thieves as he has a surprise for them. While Masaru and the other Detectives are very suspicious of Kuonji's motives, Uromu decides to accept the invitation to see what will happen. As a "security measure" music plays in every room in the Musical Box House whenever a room door is opened after midnight. Each room has its own specific tune, so you know immediately which room door is opened. During the night, everyone is awakened by a sudden tune and they all go out in the hallway. Only one person doesn't appear, who has a room on an upper floor. It was of course their room tune that played, and when they open the locked door, they find that person dead inside their room, stabbed in the stomach and no weapon inside the room. But because a tune plays immediately once the door is opened after midnight, everyone in the house seems to have an alibi because they all appeared in the hallway from their own rooms immediately after the tune of the victim's room upstairs started playing.
Within the narrative of The Last Case of Kannagi Uromu, there are all kinds of small details that pique your interests and other clues that aren't explored in the novel itself, and those are the things the members of the Detective Club focus on in the modern day while building their solutions. What is satisfying about this novel, for example in comparison with The Poisoned Chocolates Case, is that each of the solutions is truly based on the same base information (the chapters quoted from The Last Case of Kannagi Uromu). The Poisoned Chocolates Case may be famous as a mystery novel about multiple solutions, but there each member of the Crimes Club usually did extra research themselves to get "exclusive" clues and information, and used that to create their solutions. That's not the case in Kannagi Uromu Saigo no Jiken, where everyone is playing with the same puzzle pieces, but they still arrive at very different solutions. And that's even if they focus on the exact same puzzle pieces as the fundamental parts of their theories. What is the most fun about Kannagi Uromu Saigo no Jiken is how sometimes the same exact clue is referred to in each solution, but still interpreted in very different manners, leading to very different solutions. Some are the good kind of ridiculous, others seem a bit too mundane, but very doable, and there's quite some variety despite this not being a super long novel. Still, it's impressive to see multiple viable solutions to an impossible crime set-up (and there are some other mysteries in The Last Case of Kannagi Uromu too that need to be addressed), all using more-or-less the same clues. Don't expect to be able to figure out all the different solutions beforehand though: as said, many of the clues are used in multiple solutions, so even if you notice an important clue, it's unlikely you'll guess all the uses, and of course, the exact order of the solutions presented in the book is impossible to predict beforehand. The final solution presented (which is of course considered the "best") has a few moments where I thought there's no way the reader is going to deduce exactly that based on the clues, but overall, it's a very satisfying novel and a great example of how to do a mystery novel with multiple solutions. The interesting thing is of course none of these solutions are by definition false solutions, as the The Last Case of Kannagi Uromu doesn't have a proper solution, so even when one solution is followed by a different one, it never feels like the first solution was unnecessary.
One of the reason I like Queen-school chains of deduction is the way it focuses on the importance of clues and how they combine together leading to hypotheses, and I think Kannagi Uromu Saigo no Jiken is a good example of that. While the chains of deductions in this book aren't like those in a Queen novel, as in, identifying characteristics of a culprit and then eliminating suspects, the way it focuses on the interpretation of clues and weaving a web between various clues is definitely like you'd expect of a Queen novel, only now used to create multiple chains of deductions which all lead to different solutions.
Oh, by the way, at the end of the book it's mentioned how this book was originally submitted to two different debuting author awards: first the Mephisto Prize in 2012, where it was one of the titles noticed by the editors but didn't get picked eventually, and again, with a new title, for the 29th Ayukawa Tetsuya Award, where it made it all the way to the final jury round, but lost to Houjou Kie's Jikuu Ryokousha no Sunadokei ("The Hourglass of the Time-Space Traveller", 2019). Sometimes, getting a book published via an award for debuting authors also involves a lot of luck and timing...
Kannagi Uromu Saigo no Jiken is a novel I enjoyed a lot. Perhaps part of it was reading it right after Spiral ~ Suiri no Kizuna 2 and seeing its influence on a book published twenty years later, but I'd say that the book is excellent even without that context. It's a very good take on the mystery story with multiple solutions, and you know, I think both sides of the story have potential become a series: I'd be interested in both earlier adventures of Kannagi Uromu and his band of detectives, as well as more of Hakuto, Shiki and Kira of the Detective Club. Anyway, very likely this will end up on my list of favorite reads of this year!