Valerie Martin's book is set in the US deep south
US author Valerie Martin has beaten the odds to win this year's Orange Prize For Fiction.
Her novel Property saw off works by high-profile writers such as Donna Tartt and Zadie Smith to land the £30,000 award.
The Orange prize is presented each year for the best English language novel by a female writer.
New York-based Martin had not been considered a likely winner among bookmakers, who preferred Tartt and Smith's chances.
But it was Martin's intensive study of relationships during the 19th Century US slave trade that most impressed the judges.
The book, set in America's deep south, centres on the life of Manon Gaudet, the unhappily married wife of a Louisiana sugar plantation owner.
It explores themes of power, ownership, resistance and freedom.
Martin - who was born in Missouri and grew up in New Orleans - has written six further novels, as well as a biography of St Francis of Assisi.
Zadie Smith had been tipped for success by the bookmakers
The other shortlisted writers were Edinburgh-born Shena Mckay, Glaswegian Anne Donovan and Canadian Carol Shields.
The Orange Prize has a reputation for picking outsiders.
Ann Patchett was the least-fancied author last year, but took the prize for Bel Canto, and Kate Grenville also defied the odds to win for The Idea Of Perfection in 2001.
Carol Shields has also enjoyed Orange Prize success before, winning in 1998 with Larry's Party.
This year's judges included model Sophie Dahl - whose first novel was released this year - and journalists Nicolette Jones and Annalena McAfee.