In a Britain of the near-future so saturated with surveillance that the government can literally plug itself into your mind, a woman called Diana Hunter is taken into custody. Her consciousness is accessed via a technology called Witness, designed to decant her thoughts and memories, thereby allowing the police to determine her level of guilt and, while they’re at it, ‘take preventative and curative measures against sociopathy, psychosis, depression, aggressive social narcissism, sadism, masochism, low self-esteem, undiagnosed neuroatypicality’ and so on. It’s a standard procedure and most people are content to undergo it. Despite Gnomon’s debt to the dystopian tradition of Zamyatin’s We and Orwell’s Nineteen Eighty-Four, Nick Harkaway’s imagined future is actually a low-crime, happy-population sort of place.

Not everybody is complaisant, though. Hunter herself is a refusenik, a cult novelist who lives in a house she has personally converted into a giant Faraday Cage, the better to evade the nosy state. When she unexpectedly dies in custody, the novel’s protagonist, Inspector Mielikki Neith, opens an investigation.

Neith begins