Bounty hunters, the manpower of western militaries and special Swiss agents were all deployed but they either met road block after road block or flew home empty-handed. Twitter flitted to the next crisis, leaving the Chibok girls to take survival into their own hands. As the days in captivity dragged into years, they became witnesses, and often victims, of unspeakable brutality that they chronicled in secret diaries. Many of the girls were Christians who refused to take the one easier path offered them - converting to Islam.

A heart-stopping thriller, a riveting narrative history and an incisive cultural analysis, Bring Back Our Girls is the definitive account of a kidnapping and digital campaign that changed our understanding of warfare, terrorism and online activism. With a plot that unfolds on four continents, from the remote forests of northern Nigeria to the White House; from clandestine meetings in Khartoum safe houses to century-old luxury hotels on picturesque lakes in the Swiss Alps, it is cautionary tale plumbing the promise and peril of an era whose politics are fuelled by the power of hashtag advocacy - and at the centre of which stand some exceptionally brave and resourceful girls.