This is a tale of two torturers. Ferrari's sepulchral chamber piece is set in the mid-1950s during the Algerian war, looking backwards to the second world war and the French defeat in Indochina, and forwards to the collapse in 1958 of the Fourth Republic. The book won several awards on publication in France in 2010, but its modern resonances go far beyond the francophone world.

Just a few pages in, you relax in the recognition that the author has made some strong stylistic and structural judgments: in other words, that he knows what he's doing. The first voice is a torturer, Andreani, addressing his comrade and superior officer, whom we know initially only by Andreani's repeated address, "mon capitaine". Geoffrey Strachan's decision not to translate this phrase is beautifully judged, since "my captain" would not capture the amorous deference of Andreani's claustrophobic wheedling, and the subsequent modulations of irony and hatred that the address undergoes in this speaker's passionate ranting. Andreani relates intimate and horrific reminiscences of torture at their military station, which he justifies with equally intimate and horrific descriptions of murders of civilians committed by their Algerian enemies: a bridal party in which everyone's throat is cut; young people at a milk bar blown to pieces.

Andreani's sections alternate with a cooler third-person narration that focuses on the captain himself, Capitaine Degorce, over a few days in 1957. Degorce has captured the leader of the rebels, Tahar, and is impressed by his adversary's serenity. Tahar seems untroubled by his own atrocities, and can perhaps help Degorce save his own soul. Degorce, who was himself tortured by the Gestapo in 1944, declines to have Tahar treated in the same manner, and instead gives him the full military "compliments". But others in the chain of command are not so keen to keep Tahar around.

Degorce is even so a torturer himself, and knows it: this is his damnation. (At one point he walks in on what his junior officers are doing: the scene is played as porno-bureaucratic farce.) All Degorce has to cling to is the practice's supposed "effectiveness". Ferrari's ingenious scheme is not to set things up in a banal way with a pro-torture character and an anti-torture character arguing the toss about the morality of torture, which would be deathly boring as fiction. Here there are just two torturers, one of whom is not at peace with what he has become.

Both men, however, take refuge in euphemism and dehumanising constructions. Andreani deploys a revealingly objectifying definite article when he describes how, after "we suspended the Arab from the ceiling", he "applied the electrodes to the ear and penis". Degorce, on learning that a colleague has captured a young woman, instructs his underling to "Come back here with your package". Late on, the despairing capitaine thinks of himself as master of a huge machine that he cannot stop; he can only keep feeding it the "organic fuel" that it demands. At different moments, both men speak of actions or thoughts as being "weightless" or lacking "gravity". Ferrari could have titled his book The Unbearable Lightness of Torturing.

The novella would fail if it were merely a static diorama of horrors, but the story has a doomy propulsion, with its elegant flashbacks and adumbrations, vivid, economical scene-setting, and fascinating relationships at its heart. It is in effect a diabolical love-triangle: Andreani loves Degorce, who does not love him back but loves Tahar instead. The suspicion arises that this knot might be eternal, as Ferrari brings events to an ending that is true coup de théâtre.

Perhaps inevitably, the devil still has all the best lines. Ferrari engineers in Andreani a terrible nihilist pseudo-wisdom and a monstrous rhetorical trickery, enabling him to claim that violating prisoners with "electricity and the knife" is the only way to show "compassion" for murdered civilians. Degorce, for his part, dully insists on calling the torture he solicits "questioning" or "interrogation", much as the Bush-Cheney administration referred to its own official torture regime as "enhanced interrogation" or being "questioned by experts". Meanwhile, Tahar tranquilly informs his captor: "A martyr is a thousand times more useful than a fighter. That's why you will never see victory." This blackly brilliant work does not insist overtly on its parallels with the recent history of Abu Ghraib and the still-operational Guantánamo Bay, but it hardly needs to in an age where torture, "rendition", and indefinite "detention" are still business as usual in so much of the allegedly civilised world.