A circle may begin at any point - with a gun, or a an argument, or a butterfly blown by the wind. When someone shoots at the President on tour in Morocco, the shock is less than the mystery. Of all the recent Presidents, why this one? What to do with the shooter, dubbed Prisoner Zero? And - increasingly urgent - who IS Zero? Prisoner Zero will say nothing, and seems to have no past. He could be Arab. He could be American. He could be insane, he could be professional, he could be a lone gunman or represent a vast conspiracy. Maybe he has more than one past. Or maybe the answer lies in the future, where an emperor waits alone in the Forbidden City, for an assassin and a butterfly. Jon Courtenay Grimwood's gripping and brilliantly clever new novel confirms what fans of his Ashraf Bey series have always known - that he is one of Britain's most innovative writers