We've seen more and more uses of AI as devices in mystery plots the last few years, though I think the best/most memorable uses of them in mystery fiction are still when they use the gap between real humans and AI to create clues etc. I've seen a few examples in the last few years that worked really well.
I mean, I guess a black box on legs can be a challenging idea for a captivating cover image, but I am also not a very big fan of the current cover now as it really humanizes the robot too much... I mean, the Jameson-type robots in Ghost in the Shell can be be cute, so it's not like having just the box robot would necessarily be boring...
The book opens the curtains with Open the Curtain, which has Utsugi visit Shindou on the recommendation of Professor Yakushi, who is examining Excimer. Shindou is an old study mate of Professor Yakushi and runs a company involved in AI technology, so Yakushi thought Shindou would be interested in meeting Utsugi, and more importantly, Excimer. Utsugi arrives the Shindou residence on a warm day, carrying Excimer in a backpack. Because Shindou had not been told much about Utsugi, he at first doesn't understand why Yakushi wanted him to meet Utsugi, but he soon realizes what Yakushi's intentions were once he learns about Excimer. The flagship product of Shindou's own company is not as sophisticated as Excimer, but a lot more practical: SILK is an AI that functions as a controlling system for all of your smart home appliances and technology, allowing you to give verbal or even non-verbal commands to control everything from the lights to the curtains or warming something up in your microwave. As Shindou and Utsugi discuss SILK and Excimer's respective uses though, Excimer starts to act weird: she has detected Shindou is a murderer and is about to kill him, but Utsugi can just stop her in time. But how did Excimer find out Shindou's a murderer during a short chat?
The reader gets a good idea of how Excimer works in this opening story: it is a detecting machine, but that is not Excimer's main purpose. Therefore, she is actually not keeping Utsugi up-to-date on her deductions, and will decide on her own to eliminate a threat. It is only once Excimer's deduction processes have identified a murderer without doubt, that she'll move in for a kill, but it's also only then she agree to tell Utsugi about what thinking process led her to the murderer. That leaves Utsugi with only a very small window of opportunity in which he can have Excimer explain her deductions: if he's too early, Excimer won't explain her (unfinished) deductions, if he's too late in issuing a "don't kill" command, Excimer will already have killed the target. Open the Curtain works as a short, but effective introduction to how this all works, as we see Excimer only become dangerous once enough clues have been shown, and while some clues were a bit obvious to see, I do like one line of clue a lot, as it fitted perfectly with the theme of the AIs. It's a pretty brilliant clue, that is used multiple times in several ways in a very short scene, yet it doesn't stand out at all. It's also a uniquely modern type of clue, which I really like. The aftermath of the deduction scene is also great, and really sets up the tone for the rest of the book.
Lost and Found introduces us to a new main character: Misa is a student who studies under Professor Yakushi and she's been offered a part-time job as the "scribe" of Excimer: she's to accompany Utsugi and Excimer and write down everything Excimer says and does as part of their research into Excimer's technology. On the day Misa visits the detective agency of Utsugi to introduce herself to Utsugi and Excimer. It turns out Utsugi owns the whole building, using one floor as his own agency and renting the other floors out. Employees of a trading company housed on a lower floor go up to the rooftop during their lunch break. They happen to look down at the empty lot behind the building, where they see a dead man on the ground, with a ladder next to him. Due to building violations, the empty lot is actually inaccessible, as it is completely surrounded by buildings on all four sides. It thus appears the man tried to cross from the rooftop of one building to another, perhaps in a burgling attempt, and then fell to his death, but is that really the case?
This is I think the longest story in the collection, and it's definitely the most complex one. The mystery revolves around whether the victim's fall was an accident (it wasn't), and if it wasn't, who pushed the man to his death? The victim turns out to be an ex-employee of the trading company, who had been fired for embezzlement, so the police suspect he was trying to break into the building via the rooftop: the building opposite the empty lot has been empty for a while, so he could easily get to the rooftop of the empty building, and then use a ladder to climb across the empty rooftop, to the rooftop of the building owned by Utsugi. While Misa and Utsugi did hear a thud during their talk, they soon suspect it was faked to create an alibi, but who then committed the crime? The story's length is used in a good manner, allowing Misa to also act as a would-be detective, offering good suggestions and theories. Her presence is certainly needed, because Excimer won't openly theorize before she gets a chance to kill the murderer, while Utsugi isn't trying to be a detective at all, leaving everything to Excimer or the police (the police works with Utsugi/Excimer, but also know how dangerous Excimer is, so it's a reluctant team-up each time). So having Misa act as a Watson Plus, with her own theories helps flesh out the story a lot, especially, as we later learn, her presence actually does have influence on how Excimer's conduct throughout this case. The solution is not mechanical in terms of how the culprit killed the victim precisely, but it does involve a plot with a lot of moving parts/necessity of good timing and is overall a very competently constructed puzzle. I do like how Excimer is shown as more and more unhinged with each story: here we learn Excimer actually actively occasionally just shows short glimpses of her answer in order to entice the police and Utsugi in letting her meet the suspects personally, which gives her better opportunities to exterminate the murderer once she has identified them! The final reveal of what clue helped Excimer determine the truth of what happened is absolutely brilliant by the way and it is this moment that for me best exemplifies the potential of Excimer as a brilliant, but amoral detective.
Don't Disturb Me has Excimer examining a past incident, involving the young brother of one of Misa's childhood friends, Fuuka. When they were very young, Fuuka's parents were invited by a friend to stay at their newly opened seaside hotel. Fuuka and her brother Haruto were still very young, and had never stayed at a hotel before. Misa was also invited, as was Riichirou, a friend of Haruto. The trip to the hotel was rather long for the children however, and Haruto was still sleeping when they arrived. Their parents brought Haruto to their hotel room to sleep some more, while the other three children went playing in the neighboring room, which had a connecting door to Haruto's room. The parents went to the lounge with the friends. However, while the other children were playing and the parents were away, Haruto fell down the balcony of the room. While it was believed to be a tragic accident, with the young Haruto waking up alone drowsy in a hotel room and accidentally falling down the balcony, about 15 years later, Fuuka now wonders who of the people at the hotel was hiding their murderous intent from the others. She asks Misa to present the problem to Excimer to see if she can solve this mystery.
Interestingly, Don't Disturb Me is the very first Excimer story: this story was originally serialized in 2024, and the other four stories in this book are written especially for the book release. The story has an interesting angle as it is mostly a flashback, following very young children who get involved in a tragic accident involving the youngest child. It's from this account Excimer manages to figure out the truth of what happened exactly and how anyone could've made Haruto fall from his hotel room, as it was technically a locked room: the corridor-side door not only locks automatically, but was also latched from inside. The connecting door between the two rooms was unlocked, but could be observed by the three children playing in the other room. And the balcony-side too can't be accessed without leaving any traces. The story places some neat clues, though I do think these stories that rely on children's testimonies/interpretation of events can be a bit hit or miss, as it is difficult to write convincingly and yet fairly that a child thought X or Y and that that had effect on the mystery. Especially when they are young and children grow up fast, it's hard to pinpoint an exact age range where you can fairly expect a child to understand or not understand X and incorporate that in a mystery plot. So that always keep bothering me when I read these kinds of stories. The theme of the past mystery however is well incorporated into the framing story of this tale, and it's a very decent entry in this collection.
You Have Control gives us a huge shake-up and shows us what can happen when Utsugi isn't there to control Excimer. One late evening, Utsugi (and Excimer in his backpack) are walking Misa back to her flat after working on a case. They meet a few of Misa's acquaintances/fellow flat residents along the way, but when they arrive home, they find a cut-off body part: a hand. Utsugi turns out to be bad with bloody bodies and passes out at the sight, but he did this at the worst time possible: Excimer is already determining who the killer is! Misa just has enough time to grab the backpack with Excimer inside and runs to her flat to lock the robot inside her room, while she tries to call the police and Professor Yakushi to see what she should do. Meanwhile, she can hear Excimer cutting the backpack open with her installed knife and trying to break out of the room in order to exterminate the threat (= the killer). Because only the now unconscious administrator can command Excimer to pause her attack and ask her about her deductions, Misa realizes she has only one option left in order to stop Excimer's murderous tendencies: she has to figure out for herself who the murderer is, and convince them to give themselves up so Excimer won't see them as a threat anymore.
The idea of this story is absolutely great, and there's a lot of tension going on as we have seen in previous stories Excimer will not lie to people, but will manipulate them in order to get an opportunity to kill a murderer. I think what is interesting is about this story is that Excimer acts as a "deductive clue" here: in reality, we know that a random murder that happened on the street doesn't mean the suspect has to be one of the people we just happened to meet outside on the street. It could be anyone whom we just happened to not meet in the city. In this instance though, the reader is informed the killer is someone we met in this story, because of Excimer's reaction. Of course, Excimer's deductions are also based on actual clues we saw in the story, but because she's such an advanced AI, the story could still get away with saying Excimer managed to solve the case based on what she saw/heard/sniffed, plus a probability calculation, giving her an edge over us humans in determining wether the killer does happen to be one of the people we met on the street. The murder itself is a bit silly to imagine, as the way the hand got cut off feels almost comic-like, but the premise of the story is just so great and it stays so exciting until the very end, I actually liked it better than the previous story.
The final story, Just a Machine, is not a straight mystery story, but acts as the collection finale. The story starts with the theft of Excimer by an unknown figure, which immediately sets off the alarm bells at the police station and Professor Yakushi, as they are all too aware what harm Excimer can do if she happens to come across a murder on the street without Utsugi's supervision. The story however then starts revealing more about Utsugi and his past with Excimer, and the mystery of how Excimer works. The story neatly picks up some strands of clues planted in earlier stories, revealing something had been brewing without the reader's knowledge, but to be honest, it's not that huge of a deal, and a lot of readers might have guessed the general gist already even if it had not been clewed. I do like how this story acts as a finale to the book.
Tantei Kikai Excimer is a short, but solid collectionthat admittedly is helped a lot by the great premise of Excimer as an unscrupulous detective AI: the stories are their best when her goals and abilities are used to shape the actual mystery plot and the way the story develops. The core mystery plots in this book are overall solid, but sometimes a bit too short or limited in scope, but having Excimer working on them usually does elevate them. It'd be interesting to see how Excimer would evolve, if sequels are to come.
