Paparoa National Park is an eerie place. It's a ledge of land perched between sea and rainforest-clad hills. It's porous and riddled with caves. It's a beautiful mass of twisted limestone. And it's just the kind of place you might run to if you're trying to disappear, or simply get off-grid and enjoy a simple way of living. One night I sat on the top of a stack of limestone pancakes, sea surging all around, letting my imagination drift. What if someone came here with a secret that would grow into an obsession? What could tip this person into becoming a killer? And how might such a story evolve? A terrifying introduction to caving made me realise just how lethal this beautiful place could be. And it took no big leap of imagination to think of the kind of people who might come to this place and the stories they could bring with them. As I wrote Cold Hard Murder I disappeared into a summer I'd spent working in this national park many years before. Revisiting it recently I was amazed by how little it had changed. On the surface at least. But my book delves beneath this into the labyrinth of caves and into the depths of my imagination.