Paris has suffered its worst attack since the Second World War, and the consequences are incalculable. Multiple shootings and bombings have left 129 people dead, and the finger of blame is pointing at the Islamic State. This edition of Panorama hears the stories of those who were caught up in the unfolding violence in Paris and looks at the emerging evidence of international links to Belgium and Syria. Emily Maitlis presents, with reporter John Sweeney.