Sophie King is missing. Her parents, Harry and Zara, are distraught; for the last 17 years, they've done everything for their only daughter. The police have no leads, and Harry and Zara are growing increasingly frantic - and increasingly obsessed with their highly suspicious neighbour. He won't open the door, he won't answer any questions. If they want answers, they're going to have to take matter into their own hands. But just how far are they both prepared to go?