Near-future Britain is not just a nation under surveillance but one built on it: a radical experiment in personal transparency and ambient direct democracy. Every action is seen, every word is recorded. Diana Hunter is a refusenik, a has-been cult novelist who lives in a house with its own Faraday cage: no electronic signals can enter or leave. She runs a lending library and conducts business by barter. She is off the grid in a society where the grid is everything. Denounced, arrested and interrogated by a machine that reads your life history from your brain, she dies in custody. Mielikki Neith is the investigator charged with discovering how this tragedy occurred. Neith is Hunter’s opposite. She is a woman in her prime, a stalwart advocate of the System. It is the most democratic of governments, and Neith will protect it with her life. When Neith opens the record of the interrogation, she finds not Hunter’s mind but four others, none of which can possibly be there: the banker Constantine Kyriakos, pursued by a ghostly shark that eats corporations; the alchemist Athenais Karthagonensis, jilted lover of St Augustine of Hippo and mother to his dead son, kidnapped and required to perform a miracle; Berihun Bekele, artist and grandfather, who must escape an arson fire by walking through walls – if only he can remember how; and Gnomon, a sociopathic human intelligence from a distant future, falling backwards in time to conduct four assassinations. Aided – or perhaps opposed – by the pale and paradoxical Regno Lonnrot, Neith must work her way through the puzzles of her case and find the meaning of these impossible lives. Hunter has left her a message, but is it one she should heed, or a lie to lead her into catastrophe? And as the stories combine and the secrets and encryptions of Gnomon are revealed, the question becomes the most fundamental of all: who will live, and who will die?