The Devotion of Suspect X, By Keigo Higashino

How do you solve a problem like murder?

The Devotion of Suspect X arrives with great expectations.

It sold more than two million copies in Keigo Higashino's native Japan, becoming what the English translation blurbs as a "national obsession".

In the opening pages, this is hard to credit. The story seems so mundane, so in thrall to routine, that Samuel Beckett might have rejected it for a lack of drama: "At 7.35am Ishigami left his apartment as he did every weekday morning." Ishigami's existence is presented as a matter of uninteresting facts:."He worked at the private high school just before the park. He was a teacher. He taught maths."

But gradually, these facts begin to add up. Insular and intense, Ishigami is a mathematical genius and one of life's great observers. What truly absorbs his attention is his next door neighbour, Yasuko Hanaoka, who works at a local food shop. Although the pair have hardly spoken, Ishigami is devoted to this single mother of a single daughter, Misato.

What is harder to understand, and what drives this novel's gripping plot, is what Ishigami's devotion actually entails. The drama arrives suddenly in the shape of Yasuko's violent, sponging ex-husband, Togashi. Yasuko snaps, but not before Misato attacks her stepfather with a copper flower vase. Convinced that Togashi is about to murder her daughter, Yasuko strangles him to death with an electrical cord. Enter Ishigami (with eerie convenience), who offers a solution, seemingly with no strings attached. "Trust me," he says. "Logical thinking will get us through this."

The premise takes 48 pages to narrate; the remaining 330 describe the ingenious cover-up and the police investigation lead by Inspector Kusanagi, with a little extramural help from the brilliant physics professor, Manabu Yukawa. Yukawa just happens to know Ishigami from university, and seems uniquely placed to read his mind.

Contrivances such as this occasionally strain one's belief. But Higashino's fictional universe is so carefully constructed and his plot so perfectly paced that these bumps in the road are quickly flattened. As with your average Columbo episode, the initial fun is in witnessing the intellectual cut and thrust between Ishigami and Yukawa – an equation that can basically be summarised as "I know that you know that I know what you know".

Gradually, the raw, emotional inter-relationships take over. Bonded by faith and deception, love and mistrust, the characters circle each other in elaborate patterns. How will Ishigami react when one of Yasuko's old flames reappears? Is he really a knight in shining armour? And just how far is he willing to go to protect her?

In the final pages, twist follows twist, turning everything on its head. The finale is both chilling and moving, and confronts emotions that crime fiction rarely covers. You realise that The Suspect of Devotion X is not simply an extraordinary thriller but a love story. A strange one, it is true, but a love story nonetheless. It will linger long in the memory.