Imagine spending thirteen years fighting and travelling in disguise in the deserts of Inner Asia, then another thirteen years as an officer in the Sikh army. Suppose, too, that while 'long separated from the world' you had acquired a reputation for conduct utterly unacceptable in civilised society. Many would reckon you a scoundrel and liar, despite your protests. Lively reminiscences - such as saving the city of Lahore in 1841 by singlehandedly killing 300 invaders - and numerous scars would not impress them.

Gardner's story, like Marco Polo's, changed people's understanding of the world. The urge to contest or authenticate his account contributed to the scientific and political penetration of a vast chunk of Asia. Readers will see the whole region, from the Caspian to Tibet, in a new light and gain a fresh perspective on its last years under native rule.

Keay's credentials for writing the biography of Gardner are unrivalled.