THE HUNGRY TIDE, by Amitav Ghosh. HarperCollins, 2004, 403 pp., £10.99 (paper).

Piyali Roy, the daughter of Bengali immigrants to the United States, is spotted standing on a railway platform. She is dressed in the clothes "of a teenage boy." The man who distinguishes her from the crowd, as a stranger and a foreigner, is a middle-aged businessman from Delhi called Kanai Dutt.

The station is in Kolkata (Calcutta), and both of these people are traveling southward, to an area called the Sundarbans. This sultry and scarcely inhabitable region is made up of mangrove swamps and the ever-changing islands that form the largest river delta in the world.

It is the place where the Ganges and the Brahmaputra flow into the sea, where the salt and freshwater tides meet and intermingle.