The Japanese are rarely half-hearted about their interests. From their delight in cute little Hello Kitty to their fascination with blood types to their addiction to karaoke, full-blooded obsessions are big in Japan. But to the outside observer these passions are usually strange and inexplicable.

The Devotion of Suspect X is different. Marketed as the book that "sold over 2 million copies in Japan and became a national obsession", this novel is a universally enjoyable thriller that is, at the same time, intensely Japanese. So even as it leads us through the bustling streets and crowded clubs of Tokyo, we meet many familiar characters - the bewildered but well-meaning cop, the almost invisible neighbour, the over-wrought teenager.

The story begins on a surprisingly pedestrian note. Yasuko Hanaoka is a single mother who works in a Tokyo bento shop, trying desperately to create a secure life for her daughter Misato. The fragile peace is shattered when her manipulative, greedy ex-husband Shinji Togashi lands up at her apartment with a slew of threats and demands.

Unable to stand his innuendoes and sneers, Misato snaps. She attacks her former stepfather with a copper flower vase. Togashi responds with unbridled violence. Determined to prevent him from hurting her daughter, Yasuko tugs him back with an electrical cord. In the process, she strangles and kills Togashi.

There seems to be no option but to call the police and confess to the crime. But then help arrives in the unexpected form of Ishigami, the mathematics teacher who lives next door. And suddenly, this sordid domestic crime acquires an unexpected dimension.

Yasuko herself has barely noticed the burly and expressionless Ishigami during the year that they have been neighbours. But behind his dour exterior, Ishigami has two great passions - his love for mathematics and his crush on Yasuko.

Ishigami uses his extraordinary mental abilities to save Yasuko and create a complex camouflage. And by the time the police stumble onto the scene, they are unwittingly playing a role that Ishigami has assigned for them. If Yasuko and Misako are being directed by a genius, the confused Inspector Kusanagi is not without his own resources. He discusses the case with his old friend, Manabu Yukawa, a physics professor who enjoys playing sleuth.

It transpires that Ishigami and Yukawa were classmates in university. It's soon apparent that the mathematician and physicist are the true forces in this intriguing drama.

The Devotion of Suspect X is an accomplished mystery with a superb twist at the end. What is entirely unexpected is that it is at the same time a moving story - a tale about finding love and devotion in the most unlikely places.