A dead girl lies on a blood-soaked mattress, her limbs spread in a parody of ecstasy. The scene matches a series of murders which ended when irrefutable forensic evidence secured the conviction of one Derek Tyler. But Tyler's been locked up in a mental institution for two years, barely speaking a word – except to say that 'the Voice' told him to do it. Top criminal psychologist Dr Tony Hill is prepared to think the unthinkable – this is not a copycat murder but something much stranger. While DCI Carol Jordan and her team mount a desperate and dangerous undercover police operation to trap the murderer, Hill heads towards a terrifying face-off with one of the most perverse killers he has ever encountered.