"I assure you that the most winning woman I ever knew was hanged for poisoning three little children for their insurance money." (Sherlock Holmes to Dr. Watson in The Sign of Four)

Early 1902: On the eve of Newgate Prison's demolition, Watson spies Holmes leaving a public sale of the prison's miscellany in the company of a beautiful stranger, and in possession of an unusual trophy–the death mask of a woman who, more than 20 years earlier, had been executed for the murder of her three children. Holmes agrees to satisfy Watson's curiosity about the memento by recounting the decades-old history of its subject.

Late December, 1878. A young Sherlock Holmes is living in a modest room at Montague Street, dividing his time between the lecture halls and the laboratories, "...studying all those branches of science which might make me more efficient". At the shop of the eccentric, old bookseller, Brodie, Holmes is introduced to the beautiful Violet Rose Turner, the young mistress and protégé of Professor James Moriarty, and the mother of his three children.

When a house fire takes the lives of Moriarty's children, it is presumed to be accidental, until Miss Turner's suspicious conduct prompts a further investigation, which reveals that the children had been poisoned before the fire was deliberately set. Miss Turner is charged with the murders. As her trial proceeds, Holmes sets out to prove her innocence, yet each of his discoveries seems only to confirm her guilt even as the court-room testimony assures her conviction. Not until the sentence is carried out does Holmes happen upon a scrap of evidence that sets off "...that mixture of imagination and reality which is the basis of my art", and leads to the exposure of a brilliant and sinister deception.

Hidden Fires is equal parts complex puzzle, Victorian era thriller, and an "origin story" that explains familiar elements of Holmes' background and character: a distrust of women that exempts the "Violets" who are always treated chivalrously, an acquaintance with the "street urchin" Wiggins, the acquisition of a priceless Stradivarius, and the real inspiration for that bullet-marked V. R. above his sitting room mantle.

Join Watson as Holmes recounts "...one of the most extraordinary narratives of my friend's career–indeed, one which may have shaped what he was to become."