The Exception, by Christian Jungersen, trans Anna Paterson

Atrocity at the office

Read The Exception on holiday, when it matters less if you can't sleep. It's a murder mystery, full of mental and physical cruelty. And it's a roman à thèse about evil, which is what will really keep you awake. It reminded me of the novels of Patricia Highsmith, and even more of Lionel Shriver's We Need to Talk About Kevin, which asked the same question - how innate is evil? The Exception lacks their literary wit and polish, but its very plainness makes it almost more disturbing.

At the Danish Centre for Genocide Information (DCGI), researchers Iben and Malene, librarian Anne-Lise and secretary Camilla study the genocides of the 20th century - which killed 60 million in purges, compared with 40 million in wars. Iben writes a long article on "the psychology of evil", in which she documents research from Hilberg and Arendt in the 1960s, through the terrifying experiments of Stanley Milgram, to the latest studies, especially Christopher Browning's Ordinary Men. Studying Nazi conscripts, Browning found that, ordered to murder women and children, a few refused, a few became eager killers, and the majority reluctantly obeyed.

They did so not out of fear of punishment, but out of respect for authority; and even more out of solidarity, a desire not to abandon - or worse, be abandoned by - their comrades. The greatest human fear is to be excluded from our group. Combined with the calculation of loss or gain, this fear will make 50 to 80 per cent of us ready to kill. After the aberration, we will repress our memories in order to live with ourselves - or even, in extreme cases, split into two (or more) selves, one with no memory of what the other has done. This is DID (Dissociative Identity Disorder), which affects victims as well. We cannot face the evil we have committed or suffered. So we justify it, or forget it; and so it can carry on.

All this Iben and the others study, and Iben experiences herself when she and her group of aid workers is held hostage in Africa. But now comes the twist that makes this such a clever and sleep-depriving novel: the four women, plus their male bosses, husbands and lovers, act out the findings of Browning and the others in their own daily lives.

Anne-Lise, the newcomer, threatens the status quo, and Malene's job; Iben and Malene unite against her, and without admitting it, bully her mercilessly. But there are tensions between the two friends - Malene is prettier and more successful with men, including Gunnar, the one Iben wants; but Malene has chronic arthritis, and fears that she will be left on the shelf. Paul, their boss, is a ruthless manipulator who collaborates with the fascist MP who controls the fate of the Centre.

Suddenly, a crisis arrives. Iben, then Malene and Camilla, receive threatening e-mails. Who sent them? Mirko Zigic, a Serbian war criminal whom they've unmasked? Iben and Malene suspect Anne-Lise. Then they discover Camilla's guilty secret, and all three suspect her instead.

Malene's computer-expert boyfriend, Rasmus, hacks into Anne-Lise's computer, then dies in a grisly accident. Iben reads Anne-Lise's notes, and realises what she and Malene have been doing. Now she, Anne-Lise and Camilla gang up to exclude Malene. Finally, Zigic captures and tortures Iben, Malene and Gunnar. He wants the disc with their information on him - plus the threatening e-mails, which we know one of the group has sent. But who? And who killed Rasmus? Though we enter everyone's thoughts in turn, we can't tell, because - just as the studies say - they all rationalise, repress, and even split under the pressure of perpetrating or suffering evil.

In the end we know. But we also know that, as Anne-Lise's doctor says, "victimising others is part of human nature". If it weren't for the eponymous exception, and the sense that the guilty hate their own evil, we would despair. Thanks to Christian Jungersen for that; and congratulations for making these fundamental questions into such a horribly vivid and fiendishly clever novel.

Carole Angier's biography 'Primo Levi: the double bond' is published by Penguin