Superintendent Lascano is a detective working under the shadow of military rule in Buenos Aires in the late 1970s. He is sent to investigate the discovery of two bodies but when he arrives at the roadside crime scene he finds three. Two are clearly the work of the junta's death squads, and so should not be investigated by the police, but the other one seems different. Lascano follows the trail, leading the reader on a tour of a Buenos Aires poisoned to the core by the military regime.

Lascano must navigate gingerly among characters symbolic of an Argentina that has lost its way: Amancio, whose privileged upbringing makes him unable to deal with the collapse of his fortunes; Biterman, the miser, embittered beyond hope by his experiences in Nazi Germany; Eva the young radical, condemned to a life on the run, death or exile, but forced to take refuge with a cop; Giribaldi, the army major, quick to help old friends, but cruel and contemptuous of everyday civilians. Buenos Aires, corrupted by the military regime, is as important a character as any other.

Lascano must uphold the law among the people and turn a blind eye to the actions of the regime, trying to bring justice to an unjust society, where some crimes are for investigation, others are not. Of course, the crime he investigates in Needle in a Haystack turns out to be one of those he should not.