Invalided out of the army at barely twenty, Jackson Small returns to England traumatised by the violent death of his fellow soldier and blood-brother Connolly. Unable to settle and incapacitated by grief, Jackson sets off on a lunatic quest, back to the Peruvian jungle in search of something he cannot even be sure is real: the lost city of La Joya, the ancient capital of a vanished empire - a place of rare wonder once glimpsed by Connolly and never forgotten.
The city is hidden in the cloud forest that hangs between the copper-green rivers of the Andes and the impenetrable jungle of Amazonia. The pilgrimage Jackson has to make to reach it will bring him into contact with worlds he has never before imagined: that of the American patriarch farming in the wilderness, a great-hearted native priest, and the love of his life. But the lethal green depths of the forest that hide La Joya turn out also to conceal other searchers, with motives far more sinister and complex than Jackson's.