Making a welcome return tonight is journalist-turned-investigative-historian,  Tim Butcher.  Tim specialises in covering awkward places at difficult moments:  Kurdistan under attack in 1991 by Saddam Hussein, Sarajevo during the Bosnian  War of the 1990s, the Allied attack on Iraq in 2003, Israel's 2006 clash with  Hizbollah in southern Lebanon among other crises. All good preparation, then for  tonight’s skirmish with Ian...

But it’s not all fol-de-rol and bon mots  ce soir. Tim’s  new, widely-praised book is a quest to find history's most famous terrorist  before Osama bin Laden... Gavrilo Princip, the teenage assassin who triggered  the catastrophic series of events that led to the First World War.

You may think that everything that could possibly be told about this  particular Bosnian Serb has already been written. Not so. Listen to tonight’s  show – and read Tim’s excellent book, The  Trigger – and you will appreciate why reviewers have been showering  it, and him, with praise. We’re indeed proud to host him tonight.