The Ordeal of Elizabeth Marsh, by Linda Colley

Historian Linda Colley first came across her latest biographical subject when she was researching Captives, her acclaimed study of Britons enslaved overseas. At first glance Elizabeth Marsh seems a curious choice, being neither rich nor notable for her achievements, but she travelled more widely than virtually any woman of her era and in the course of her globetrotting "was repeatedly caught fast in geographically wide-ranging events and pressures". The result is what the author calls a "global biography": one that places her heroine in the context of the vast social shifts of her age.

Born in 1735, Elizabeth Marsh was one of those people to whom history just kept happening. She was conceived in Jamaica, a small but imperative cog in the expanding Empire. She made the first of her journeys in utero to England, her father's homeland. He was a ship's carpenter and her mother a young Creole widow. The family settled in Portsmouth, where the constrained circumstances of life in the "lower middling" strata were obviated by a well-placed uncle whose patronage improved relatives' opportunities and wealth financed their children's education.

In 1755, when Marsh was 20, he procured a new position for her father in Menorca. She chose to accompany her parents, but the following year made the return journey to England alone. Her ship was captured by pirates and she ended up a hostage of the Sultan of Morocco, Sidi Muhammad. Realising that the Sultan planned to add her to his seraglio, Marsh deployed both flattery and subterfuge (pretending marriage to her fellow captive, James Crisp) in order to escape concubinage. But even though there was no sexual misconduct, the interlude irretrievably tarnished her reputation. She was, after all, a young woman who had travelled without an escort, spent time with a notoriously priapic - and not unattractive - foreigner, and pretended to be married to a man who was not even her fiancé.

The only solution was to marry James Crisp in reality, which he enthusiastically agreed to do. Her marriage to the prosperous young trader was initially auspicious. They bought a house in London, had a couple of children and spent money freely. But the life of a wheeler-dealer in 18th-century England was as precarious then as today and Crisp's more questionable dealings - smuggling - brought him down. Officially bankrupt, Crisp and his mortified wife migrated to Florida where they embarked on a doomed land-development scheme.

The Crisp family had run out of chances. He fled to India to reinvent himself, and Elizabeth and her children moved back to Chatham. Desperate and hard-up, she published an account of her adventures in Morocco. The Female Captive was a commercial success, though one reviewer, hoping for more salacious revelations, sniffed that it "contained no very interesting incidents". But its author was financially afloat and she used the funds to set off in pursuit of her husband.

On arrival in India she sent her daughter back to England, while her son came out to join her. The boy arrived "almost destroyed with vermin and filth", and was swiftly apprenticed to a Persian merchant. Unable or unwilling to rekindle the marital fires, Elizabeth, now in her forties and unencumbered by childcare, decided to go travelling throughout Eastern India with a "cousin". Her diary, replete with tales of balls and card parties, does not reveal the nature of her relationship with this man. Colley, who speculates about the lax morals of the Anglo-Indian scene, makes it clear what kind of relationship she believes it to be. Though the travels continued, the final act of Marsh's life saw her resettle in England, where she ended her days.

Dramatic though Elizabeth Marsh's story is, it never quite delivers the emotional impact one would expect. This is partly due to a lack of material: there are no surviving letters and Marsh's diaries are not of the revelatory, soul-baring variety that evoke empathy.

There is also an emotional distance that seems deliberate: Colley's goal is to tell a global story first and an individual narrative second. She has turned on its head the convention of traditional biography, in which political and economic forces are analysed in order to elucidate our understanding of the subject, in favour of using an individual story to illustrate our global past. The most fascinating parts are Colley's brilliant, eclectic asides: intellectual seasoning on the motivations of migration, or the role of the Navy in the expansion of empire, or the class constraints on women's travel writing.

This book is also important in another way. Instead of being born of the labyrinthine archives so intrinsic to biographers' lore, it is a product of the internet and other new technologies that allow the historian and "anyone else" to explore manuscripts, literary catalogues and genealogical websites across the world. This new breadth of access, Colley reminds us, would be inconceivable even a decade ago. "The ongoing impact of this information explosion on the envisaging of history, and on the nature of biography, will only expand in the future."

Andrea Stuart's 'Josephine: the rose of Martinique' is published by Pan