In an alternate England, where people who are wicked in thought or deed are marked by the Smoke that pours from their bodies, Thomas, Charlie, and Livia notice that some people appear to be able to lie without triggering Smoke. As they dig deeper, they discover teachers who have mysterious ties to warring political factions, a sumptuous estate which hides attic rooms and laboratories, revolutionaries who are fighting against a secret police force. They begin to suspect that everything they have been taught about Smoke is a lie; but if that is a lie, what else about their world is lies? What is their place in the struggle between faith and reason, between good and evil? And who can they trust?