The investigative reporting of Patrick Radden Keefe has already given us non-fiction classics like Say Nothing and Empire of Pain. In London Falling, he turns his eye to the story of Zac Brettler, who plunged to his death from a luxury London apartment at the age of just 19. What his parents then discovered was an alternative life that had led their son through the capital’s dangerous underworld to that Thames-side balcony. We spoke with him about what makes a story compelling, his conversations with Zac’s parents, and what ultimately led to that fatal fall.