Mostly the books I discuss, even if they have a translation, are little known in the west. In this case most English speaking mystery readers probably read the book long before I got round to it, since 東野 圭吾 (HIGASHINO Keigo) is one of the few successful Japanese mystery exports, with several of his books now available in translation. In Japan too, 容疑者Xの献身 (yougisha ekkusu no kenshin, The Devotion of Suspect X, 2005) was one of his most successful works, winning the Honkaku Mystery prize and adapted into a film.
The book is part of a series, in which Tokyo policeman KUSANAGI (草薙) consults his old university friend, now a physics lecturer, YUGAWA Manabu (湯川学) for ideas on difficult cases. I've read an earlier short story collection 予知夢 (Yochimu, Prophetic Dream, 2000) and 聖女の救済 (seijo no kyuusai, Salvation of a Saint, 2008). The former is fairly conventional, a set of mysteries with a slight appearance of the supernatural to them. Salvation of a Saint however is an inverted mystery, like its predecessor, The Devotion of Suspect X. Perhaps it would be better to call them semi-inverted mysteries. We know (or at least we are fairly sure) who did the crime; but exactly what they did is still a mystery. As in other inverted mysteries, we follow the story both from the point of view of the detectives and from that of the criminals, with divided sympathies and some unease at the developments.
In The Devotion of Suspect X, the killer is a mother, HANAOKA Yasuko, living with her teenage daughter after divorcing her abusive husband. A threatening visit from him escalates into a fight in which they end up strangling him. (I'm not quite sure what the legal status of the crime would be in England; the events are close to, but not quite eligible for a 'self defense' plea.) They are on the point of calling the police to turn themselves in when their neighbour, maths teacher ISHIGAMI rings the doorbell. He immediately deduces what has happened and offers to help them, if they intend to conceal the crime. When they accept, he takes charge of the situation and sets to preparing a trick to deceive the police.
From the police side, we follow Kusanagi as he investigates the ex-husband's murder, soon closing in on the mother and daughter. By coincidence, the neighbour Ishigami, whom he questions as a witness, turns out to be an old friend of Yukawa. Yukawa is surprised to learn that Ishigami, a mathematical genius, is now a high school teacher and visits him to renew their friendship. Soon the various parties are separately pursuing their suspicions or concealing their guilt. Meanwhile we, like most of the characters, don't know quite what trick Ishigami used; and this is the mystery part of the book.
From Ho-Ling's post about the book, I gather that there was some discussion in Japan about whether the mystery part of the book was fair play. This seems really bizarre to me, because the solution, while shocking, is really very obvious, and pointed to by a variety of hints. It may be that the answer is more obvious if you come to it from reading Salvation of a Saint, since the narrative trickery used to mislead us is much the same. (I hope it's not giving much away to say that in both Higashino uses our insider knowledge of the criminal and their crime against us.) Seeing through the tricks (both Ishigami's and Higashino's) doesn't make the story less interesting, as the mystery is only part of the book. It does make it more painful reading though. You share more of Yukawa's distress as he pursues his friend. I don't notice anyone else claiming to have solved it easily, so if you want a challenge, don't read Salvation of a Saint first. And if you only read one, read this one; it's far the better book.