With the city of Exeter ravaged by an outbreak of the 'yellow plague', Sir John de Wolfe, the county coroner, must divide his time between visiting his brother Willam who has been struck down by the disease, and dealing with a series of brutal murders which appears to be linked to a revival of heresy in the city. When some of the cathedral canons begin a crusade against this danger to the Church, Sir John is accused of being too sympathetic to the heretics, bringing him into conflict with the ecclesiastical authorities. As the situation worsens, the coroner finds himself having to seek sanctuary in order to save his skin.