Having his childhood friend killed by one of the bizarre serial murders unsettling suburbia recently, Amane Sanshirou attempts suicide. However synesthete and detective Otomiya Miya prevents this and they end up investigating the serial murders together.
While the premise of the case itself and the investigation are rather simple compared to fancy settings as for example an isolated island or mansion (yes I want to be fair by mentioning this comparison, especially since this is a rather subjective matter), Amane Ryou does a fairly good job on weaving the topic of synesthesia into the detective figure. You can see he researched accordingly (he also references specific literature) and furthermore the detective's condition also has an effect on the structure of the plot. Miya sees sounds as colours and since synesthetic connections stay the way they are for each synesthete Miya is convinced of a certain character's guilt when she hears his voice. Therefore we always have her reasoning approach based on her presumption, her employer Yahagi's approach simply based on the facts and Sanshirou's 'watsonian' approach (Miya insists on him being like Hastings though), which is also influenced by his emotions and personal presumptions.
Kind of unexpected though is that Miya's condition does not actually come in handy all the time. Her degree of synesthesia exceeds her mental eye and she can not chose between the things she actually wants and does not want to see if she is not wearing custom-build contacts. Furthermore the way Amane writes it her deductions sometimes just resemble classical detectives' ingenious unexplainable epiphanies and there are enough cases where such a detective is also convinced of the importance of a certain clue or the guilt of a certain character and focuses accordingly during further deduction. Due to this the detective's rather unusual condition never totally deconstructs the story in way that it would not be detective fiction anymore.
All the guessing and deduction and the main characters' interaction mostly were an enjoyable read but what really turned the story around for me was the finale. Not only was the solution more surprising than I expected, until that point I did not even realize that there were so many foreshadowings hidden in the events that happened before even though I already knew that Amane likes and uses foreshadowings himself. It was crazy to be honest, but in a pleasant and amusing way while still not being unrealistic. Apart from that there is still the topic of synesthesia and different perceptions and perspectives in general, if you are not satisfied with the case, which is skillfully elaborated on over the course of the novel.
With Amane being a seemingly huge fan of Poirot and considering certain devices used in this first volume, I expect the next one in the series written around Otomiya Miya to be fairly different. Maybe I'm also expecting too much by believing that but I guess it is natural to not expect an author to write the same specific formular again... since that would be kind of masochistic for his career right after his debut work. I know, I am being naive... but I will definitely try out the next (untitled as of now) volume coming out some when in June. I can imagine a rather classical setting like a closed environment or even an isolated location to be interesting and refreshing with a detective like this.