The King's Last Song, by Geoff Ryman

Towards the end of this long but inordinately readable novel is a medieval battle of epic proportions, stretched over 70 pages. The 50-year-old Jayavarman VII, on his way to becoming the celebrated ruler of the powerful Cambodian kingdom of Angkor, fights a campaign against Champa, a Vietnam-based state that during the mid-12th century had subjugated the Khmer peoples. Jayavarman the destroyer triumphs, reclaims the city of Angkor, but then, influenced by his senior queen Jayarajadevi and her sister, creates a model Buddhist society with public welfare and the loosening of the caste system high on the agenda.

The battle sequence is extraordinary in its detail, colour and brutality, and seems sourced in the friezes that adorn temples of the period, as well as in Geoff Ryman's fertile imagination. But this is only one brilliant sequence in a book of brilliant sequences, some derived from earlier episodes in the lives of Jayavarman, Jayarajadevi and the king's slave concubine "Fishing Cat", others from contemporary Cambodia, and from the survivors of the Pol Pot and Khmer Rouge era.

The King's Last Song, then, portrays two different Cambodias, separated by 800 years, yet hauntingly interconnected. The narrative link is a set of 155 gold "leafs" or disks, on which are inscribed Jayavarman's final testimony. Buried after their dictation to a deformed son Jayavarman has fathered by Fishing Cat, they are no sooner unearthed in 2004 than stolen by a former Khmer Rouge cadre, Saom Pich. As well as seizing the golden tablets, he kidnaps their custodians, a Cambodian general and Luc Andrade, director of a UN archaeology project on secondment from an Australian university.

Luc is a closet gay who has grown up in the 1960s Phnom Penh of King Sihanouk. Held in miserable conditions on a boat on Tonle Sap lake, he agrees to translate Jayavarman's archaic "song" into a modern idiom that all Cambodians can understand. He is the only outsider who figures prominently. Past or present, every other principal character is "native", and Ryman displays an uncanny ability to get inside the minds and hearts of each one, whether the "motoboy" William, touting for tourists in Siem Reap, Saom Pich himself or, most penetratingly, Map.

Another former Khmer Rouge, Map has turned coat more often than he chooses to admit, and for him killing and skulduggery are second nature. Far more than Luc, Map is the "hero" of Ryman's novel, because through him Cambodia finds its most meaningful expression. He is the bad guy who disturbs and moves us, and defeats himself with an inner emptiness he knows is beyond redemption.

There is a hint in the structure that Map may be Jayavarman's re-incarnation. But no more than a hint: if individuals are reborn, it's because their culture is recycled.

The selfless utopianism of Buddhism is central to Ryman's exploration of Cambodian themes; but he is too steeped in his material, and too artful a storyteller, to assay the facile punch. Rather, his intricate, double-sided tapestry is woven with ambiguities that mesmerise. The King's Last Song takes some liberties with remoter history, but its leavening of invention with compassion is as good as it gets.

Justin Wintle is writing a biography of Aung San Suu Kyi