It's the execution that received a paltry four stars. The idea is brilliant and disturbing: what are the logical consequences of discovering that a specific genetic trait, identifiable through mass testing of the population, correlates with (or causes) serial killing? Kerr imagines such a situation, and in this plausible near-future world one of the men with this trait decides to make a series of pre-emptive strikes on his cohorts.
I would have liked to see a deeper engagement with the philosophical ramifications of this. There is plenty of philosophy here, but it's relatively shallow (perhaps inevitable in a novel that has no pretensions of being a treatise). My largest complaint is that there's doubt even at the end whether the perpetrator is in fact completely sane. This dulls the impact of the self-fulfilling prophecy (tell an otherwise law-abiding man he's genetically predisposed to serial homicide, and what do you think he's going to go out and do?), and also of the moral problem. The narrator of Walker Percy's "Lancelot" is a fascist, but at least he doesn't think he's his own pseudonym. (Incidentally, this is perhaps the least plausible part of the novel: upon being diagnosed, the soon-to-be killer is given by the government the alias "Wittgenstein," a philosopher with whom he has so much in common, and with whom he identifies himself so closely, that he may become delusional, at times thinking he is in some way Ludwig Wittgenstein. What are the odds of him getting that one name out of all the possible aliases? Please.) The novel would have been much stronger, and its message much more disturbing, had only the killer been clearly sane. Then the contrast between the retribution-minded government and the prevention-minded killer would have been more interesting. Then the reader would have to take seriously the killer's conclusions drawn from premises of existentialism and utilitarianism. Kerr leaves a way out for the reader ("the man's crazy!") that he shouldn't have allowed.