Dark Passages: Math that’s lethal

It’s easy to get hung up on distinctions between mysteries and thrillers (not to mention the catch-all category of “crime fiction� that often acts as an acceptable substitute) when books, especially those published today, slide fluidly between the two alleged camps. But here’s where I create an arbitrary demarcation line: thrillers create suspense through momentum, with the stakes raised higher at every conceivable point. Mysteries create suspense through deduction and the intellectual capacities of a protagonist, either a professional detective — private or governmental — or an amateur, acting on his or her own behest or that of somebody else.

The mystery novels that came of age in the Golden Age fell out of fashion as writers concentrated more on character, emotion and setting. They still do, of course, with the best so good that they create literature from genre trappings. More recently I’ve noted, if not a resurgence, then a few examples of a welcome return to the intellectual puzzle aspects of a good, plot-driven mystery.

Take “Think of a Number,� John Verdon’s debut crime novel published last summer. There’s a serial killer and a tortured ex-profiler protagonist, one whose relationship with his wife is a key emotional component of the novel. But the mystery unfolds with clever clues, daring the reader to guess each twist and to stay on his or her toes anticipating what comes next. The play is more than fair, and the resolution makes perfect sense in hindsight but delivers the requisite gasp upon first discovery.

Now another excellent brain-knot of a mystery novel arrives from the opposite side of the world. In Japan, Keigo Higashino is heralded as one of the country’s greatest best-selling crime writers. Literary emigration to American crime fiction soil hasn’t been as widespread there as, say, in Scandinavian countries, but select writers, such as Natsuo Kirino (read her brilliant novel “Out�), Miyuki Miyabe (“All She Was Worth,� “Crossfire�) and Shuichi Yoshida (“Villain�) have made their mark here to varying degrees.

Now it appears that Higashino will find his U.S. audience after a false start with 2004’s “Naoko,� a mind-and-genre-bending exploration of marriage, psychological breaks and murder straight from the school of Ira Levin. “The Devotion of Suspect X� (Minotaur, 298 pp., $24.99) is cooler, more considered and more authoritative in both voice and story, challenging the reader to pay attention to every detail before the inevitable rug is pulled in one of the most clever endings I’ve read in some time.

Far be it from me to spoil that pleasure, but luckily there’s lots more cleverness that can be discussed. We must first begin with Ishigami, once a budding prodigy, now an introverted teacher of mathematics whose intellectual ambitions grow further distant from the daily demands of his job. Upon hearing loud and violent screams from his next-door neighbor’s door, he elects to throw himself squarely into the situation. That might not seem clever at first, since the situation is murder and the victim is the abusive ex-husband of Yasuko, who just wanted to get the man out of her life once and for all.

But soon Ishigami is all logic and deduction, impressing Yasuko with his reconstruction of how the murder happened despite the soundproofed building: His solution (thumping noises + her disheveled hair + a lack of cockroaches) causes Yasuko to conclude, “he’s terribly levelheaded, and smart.�She feels encouraged to trust that he’ll make sure she avoids arrest and a long prison sentence: He has a master plan all cooked up. “Trust me,� Ishigami implores her. “Logical thinking will get us through this.�

Those ingredients include a burned-out corpse, alibis and receipts that check out, and adherence to one of Ishigami’s favorite mathematical proofs, “the P=NP problem,� which asks “whether it’s more difficult to think of the solution to a problem yourself or to ascertain if someone else’s answer to the same problem is correct.�

Such seemingly philosophical thinking goes against the mindset of Detective Kusanagi, who wants to solve what proves to be an increasingly frustrating case, with logical suspects ruled out and plausible situations rendered impossible. But it jibes completely with the thinking of Dr.Yukawa, acquainted with Ishigami during their college years and who understands all too well that mathematics and human behavior should align, but can be thwarted by emotion-based decisions.

The nexus of reason and emotion is why “The Devotion of Suspect X’s� denouement packs such a potent punch. All his life Ishigami has attempted to adhere to mathematical principles, seeking truth in elegant proofs and solutions to difficult theorems. But murder does not fit neatly in boxes offered by complex formulas, where passion, sympathy, jealousy and maternal instinct all act as disruptors. And in chilling fashion, Ishigami is left to ponder why “there would be no particular meaning to his death…just like there had been no particular meaning to his life�—and why, rather than nihilistic comfort, it cuts him to his very core.

Weinman blogs about crime and mystery fiction at https://www.sarahweinman.com. “Dark Passages� appears monthly at latimes.com/books.