Which is harder: Devising an unsolvable problem, or solving that problem?” posits Keigo Higashino in The Devotion of Suspect X. Perhaps the hardest thing is to recognise the moral ambiguity that underpins life — the things one can do for love or hate; out of guilt, shame, vengeance, and sacrifice. In part, of course, Higashino was following tradition. But Higashino’s achievement lay in his refusal to indulge certainties, breaking down, one deduction at a time, what circumstances make the crime conceivable and whether justice can ever be separated from empathy.