In 1965, when the young French ethnologist Francois Bizot arrived in Cambodia, it was a land 'rich and beautiful; partitioned with paddy fields, dotted with temples, this was a country that had chosen peace and simplicity'.

The Gate is Bizot's account of the end of that idyll. In 1971, he was living with his wife and three-year-old daughter in the northern Angkor region, studying Buddhism and attempting unsuccessfully to ignore the rising tide of war spilling into Cambodia from neighbouring Vietnam. On what was supposed to be a routine visit to a local monastery, Bizot and two Cambodian colleagues were ambushed by Khmer Rouge soldiers.

With their arms tied at the elbows behind their backs, they were frog-marched deep into Khmer Rouge-held territory by gun-toting adolescents. Accused of being a CIA spy, Bizot was detained and interrogated for three months in a torture and holding camp run by a man named Douch, who was to gain infamy as one of the Khmer Rouge's most ruthless and prolific executioners, responsible for thousands of deaths.

Bizot was the only one of 30 Westerners taken prisoner by the Khmer Rouge during the war to survive, thanks largely to the peculiar personal relationship he was able to establish with Douch.

In a recent interview, senior Khmer Rouge leader Khieu Samphan praised Bizot's portrayal of the Khmer Rouge, and of Douch in particular, for its accuracy.

From here the story jumps to 1975, and the fall of Phnom Penh. As depicted in the film The Killing Fields, Bizot and thousands of others took precarious refuge behind the walls of the French embassy as the Khmer Rouge swept into the city. Bizot, a fluent Khmer speaker, acted as intermediary between the occupants of the embassy and the unpredictable Khmer Rouge leaders.

The Gate ends with an epilogue written in 2000. Bizot returns to Cambodia and establishes contact with Douch, now a prisoner himself and facing charges of genocide. With the help of a map hand-drawn by his former captor, he visits the site where he was held and where, Douch confirms, the two Cambodians arrested with him were clubbed to death. His guide tells him, with a laugh, that he is the only prisoner to have made such a pilgrimage, simply because he is the only one to have left the camp alive.

Understandably, Bizot confesses he has written this book 'in a bitterness that knows no limit. A sense of hopelessness runs through it.' His anger is directed in equal measure at the arrogant, cynical American invaders of Southeast Asia, the psychotic Khmer Rouge murderers claiming to act in the name of the peasants they slaughtered, and the naive European socialists who feted the Communist guerillas as brothers in arms against capitalism, refusing to acknowledge early reports of atrocities.

The Gate does not follow a comfortably logical plot nor reach a satisfying conclusion. For Bizot, the ghosts will never rest, and humanity will never redeem itself. 'I no longer believe in anything except things ? do the most enlightened philosophers not teach us to mistrust man? ? A slayer of monsters, a monster himself.'