On a summer morning in Sarajevo a hundred years ago, a teenage assassin named Gavrilo Princip fired not just the opening shots of the First World War but the starting gun for modern history, when he killed Archduke Franz Ferdinand. Yet the events Princip triggered were so monumental that his own story has been largely overlooked, his role garbled and motivations misrepresented.

The Trigger puts this right, filling out as never before a figure who changed our world and whose legacy still has an impact on all of us today. Born a penniless backwoodsman, Princip's life changed when he trekked through Bosnia and Serbia to attend school. As he ventured across fault lines of faith, nationalism and empire, so tightly clustered in the Balkans, radicalisation slowly transformed him from a frail farm boy into history's most influential assassin.

By retracing Princip's journey from his highland birthplace, through the mythical valleys of Bosnia to the fortress city of Belgrade and ultimately Sarajevo, Tim Butcher illuminates our understanding both of Princip and the places that shaped him. Tim uncovers details about Princip that have eluded historians for a century and draws on his own experience, as a war reporter in the Balkans in the 1990s, to face down ghosts of conflicts past and present.