As one of the UK's leading commentators, David Wilson shows how some serial killers stay in the headlines whilst others rapidly become invisible - or 'unseen'. Yet Mary Ann Cotton is not just the first but perhaps the UK's most prolific female serial killer, with more victims than Myra Hindley, Rosemary West, Beverly Allit or male predators such as Jack the Ripper and Dennis Nielsen. But her own north east of England and criminologists apart, she remains largely forgotten, despite poisoning up to 21 victims in Britain's 'arsenic century'. Exploding myths that every serial killers is a 'monster', the author draws attention to Cotton's charms, allure, capability, skill and ambition - drawing parallels or contrasting the methods and lifestyles of other serial killers from Victorian to modern times. He also shows how events cannot be separated from their social context - here the industrial revolution, growing mobility, women's emancipation. And concerning the reticence of 'human nature', Like Dr Harold Shipman, Cotton was allowed to go on killing despite reasons to suspect her.The book contains other resonances to aid understanding of how serial murderers can continue to kill despite such things as coincidence, gossip, whispers or motives that become more obvious with the benefit of hindsight.It is also a detective story in which the persistence of a single individual saw Cotton tried and executed, events analysed first-hand and in detail from the records.