When the body of an Australian backpacker is found in Spain, an online group of amateur true crime sleuths springs up around the world, attempting to solve the mystery of her death. Foremost on the message boards is Astria, a young Norwegian woman whose feverish pursuit takes her closer than anyone to solving the case. But just as she makes her claim of unravelling the mystery, she goes offline. No one in the group has heard from her since. When William Wisting is sent to investigate, he is plunged deep into a fascinating world of unorthodox investigators, whose connections are as vague and varied as their abilities. But in a dangerous case where nothing is as it seems, these online detectives may be the best hope he has for solving the mystery - before another victim falls.