Crime drama featuring the pioneering 19th-century detective Jack Whicher. After leaving the Metropolitan Police, Whicher saves a respectable country lady from a violent robbery in a dangerous quarter of London. Susan Spencer is desperately hunting for her vulnerable niece Mary, who came to London in search of Stephen Gann, the young man who had made her pregnant. Susan commissions Jack Whicher as a private inquiry agent to find her niece and the young man. Soon, Whicher is irresistibly drawn into a disturbing and puzzling murder case, bringing him up against wealthy and powerful figures and throwing him into conflict with his former colleagues in the Metropolitan police. The investigation leads to a private lunatic asylum where Whicher himself must confront the darkness of his own demons.

The elder one of each generation in the Furlong family is equipped with an extraordinary capacity. James discovers the nature of his at the time of an accident which causes the death of his father and his grandmother. Haunted by this mysterious evil he hides in a forest not to harm anybody. A few years later, Mae also takes refuge it in the forest and meets James.