A good “howcatchem” – the structure of a detective fiction story in which the perpetrator and the crime are known from the get-go, as opposed to a “whodunit”, in which such information is often only revealed towards the end – I think is premised upon two features: first, the (climatic) convergence or meeting between the detective and the perpetrator; and second, the resolution, particularly the explanation for a red herring or a sequence of events. And also, what matters more than realism in this resolution, to me, is reasonableness.
These two features could happen at the same time, yet in Keigo Higashino’s “The Devotion of Suspect X” they are separated chronologically by a few further developments. Overall, the battle of wits between mathematics teacher Tetsuya Ishigami and physicist Manabu Yukawa – two unlikely and brilliant parties implicated, in different ways, in a murder case – is compelling, drawing the reader to look for clues or slip-ups within the narratives. This is perhaps best summarised in their frequent references to the P = NP mathematical problem, which asks whether it is harder to devise an unsolvable problem, or to solve that problem. In these references, with Ishigami as the one creating the problem and Yukawa trying to outmanoeuvre his former classmate to solve the crime, even though a sense of inevitability lingers, Higashino does enough to keep the reader guessing how the resolution might play out.
And this is where the book might be disappointing for some. There are two parts to the resolution (and it is hard reviewing this feature without giving too much away), one of which seems more preposterous than the other. Aspects of this resolution are hinted at throughout the investigation process – an observation made after completion of the book, of course – and it is pieced together nicely at the end. Overall, the murder case and its premise were laid out logically, the story is paced well in the middle, towards that (climatic) convergence (even if a little rushed at the start), and even with a slightly unrealistic ending the read was still enjoyable.