There is no reality where students would gladly say yes when their Philosphy professor invites them to their office to talk about Ellery Queen and the philosophical problems regarding mystery fiction...
They leave the others in Sumiyoshi's office and walk to Seminar Room 1 on the same floor, which is unused at the moment. Just before they enter, a different professor wants to discuss something with Sumiyoshi, so Naoko enters the room first. As the two professors walk away, they notice a guard also entering Seminar Room 1. Meanwhile, Hikawa and the two girls who remained also loaf around a bit, going to the bathroom before they'll leave, but then a loud cry comes from Seminar Room 1. Everyone runs to the room, and they find... a dead guard lying in the room. But for some reason Naoko is not here. Around the same time, the police arrives at the campus, even though nobody here called for them yet, but it turns out someone else called because they saw something outside: the body of a woman was hanging from the roof of the building. This woman of course turns out to be Naoko, who was tied by her legs and thrown from the roof, hanging her upside down with her skirt hanging upside down. But when did Naoko leave the Seminar Room, why is there a dead guard there, and why was Naoko herself too killed? Hikawa, who has solved a few cases before, of course wants to know the truth, but it turns out Miho herself might be an even sharper detective than himself in Hikawa Tooru's 2001 novel Saigo Kara Nibanme no Shinjitsu or The Penultimate Truth.
After Makkura no Yoake and Misshitsu wa Nemurenai Puzzle, it was very clear that Hikawa (the actual author) is a big fan of (early) Ellery Queen, writing in the same style, and of course, Saigo Kara Nibanme no Shinjitsu follows the same idea. However, I feel that after the more exciting second novel, which utilized a closed circle situation to keep the story tense, Saigo Kara Nibanme no Shinjitsu was surprisingly boring to read, with an incredibly slow mid-section. As much as I love Queen-style detective stories, with an emphasis on longer chains of deductions based on physical evidence and the knowledge of what characters did or could have been aware of at what time, these kind of novels do rely a lot on presenting this kind of data to the reader, so the investigative portions of a story can feel a bit dragging. Saigo Kara Nibanme no Shinjitsu is an example of a book where the mid-section indeed suffers from this mode of writing, because it's just slowly feeding you data, and in a very passive way. Like in the first novel, Hikawa soon gains the trust of the police detective in charge of the investigation, who then occasionally gives Hikawa confidential information, and Hikawa has a few talks with the suspects, but all of this moves very slowly.
I think Hikawa (the author) tried to battle this by introducing the rival character of Miho, similar to the character Komiyama in the previous novel: in the second novel, the editor Komiyama turned out to be a talented fan of the mystery genre who pro-actively wanted to solve the mystery, and Miho too turns out to be very sharp, capable at times of out-thinking Hikawa (the character). But their battles only really become meaningful near the end of the tale, as Hikawa has a kind of inferiority complex regarding Miho throughout the tale, meaning it's just Miho sometimes posing a (clever) theory and Hikawa just reacting in awe and admiration. Perhaps it's because I read Misshitsu wa Nemurenai Puzzle and Saigo Kara Nibanme no Shinjitsu basically one after another, but the 'Hikawa feels inferior to rival' part of both stories felt very similar, so it was also not as exciting anymore (that, and you already know Hikawa's the series detective...)
Anyway, this time Hikawa is once again facing a situation that is not quite an impossible situation, but only nearly one. Nobody was constantly watching Seminar Room 1's door, but they can't figure out why the guard went in the room and ended up dead, while Naoko somehow ended up dead on the roof. Examining the timelines and noting the time the body of Naoko hanging from the roof was discovered by a taxi driver passing by the campus, they also realize Naoko must have left the room very early, creating only a small frame of time in which the murder could have happened. Meanwhile, there were only a handful of people left in this particular university building. In a way that's incredibly convenient for a detective story, it turns out the security company in charge of the building had secretly built an experimental system that logs the time and duration any time any door in the building is opened, which allows them to determine around which time Naoko slipped away out of the room, but again, this creates problems with the time needed to kill the guard in the room, and kill Naoko on the roof. Due to the system, the police also knows exactly how many people were in the building at the time, but not everyone with a connection to Naoko (mainly the people on the philosophy floor at the time of the murder) have a clear alibi.
As you can guess, the story becomes quite focused on deductions based on time, on figuring out where there's a gap in everyone's alibis which would allow them to commit the murder, and I have to admit, this can be quite boring. There's not much of physical evidence around, so you don't get much of those evidence based chains of deductions I tend to like, where you have to figure out why an object was used or what the use of a certain object tells you about the killer. Time table-based deductions can be interesting in combination with other elements, but on their own, or at least as the main focus, they tend to be very dry puzzles, and that's the same here, and part of the reason why this is definitely my least liked Hikawa novel of the three I have read now. Not that it is devoid of clever parts: the deductions regarding why Naoko was hung upside down from the roof are pretty interesting and exactly the kind of chains of reasoning I do like to read about, but it's definitely just a smaller element of a book that is more focused on time. The way the rivalry between Hikawa and Miho is also resolved in an interesting manner, that ties back in a meaningful manner to the discussion on Late Queen Problems mentioned earlier in the novel. Considering there's a second detective character, you know one of them will pose an incorrect solution at some time, but the way it's framed here, it doesn't feel like just filler or a fake, but it feels like an interesting thought based on the earlier philosophical discussion.
But on the whole, Saigo Kara Nibanme no Shinjitsu is certainly not my favorite of the Hikawa novels until now. While I appreciate the mode of the detection utilized in these novels, the way it is told now is a bit longwinded and I am in general not a super big fan of stories that require you to fill out time schedules for a dozen of characters and try to find a logical gap in them. Hopefully, the next will bring back some of the more focused mid-section like the second novel had.