An attack in February, 1902, upon Henry Bamford, an eminent forensic photographer, brings him to seek out Holmes' help, However, even as Holmes is considering the case, Bamford is cruelly murdered. Holmes feels a measure of guilt from his inaction and is joined in finding the killer by Bamford's house guest, a young Frenchman, Edmond Locard. Locard is an aspiring criminologist and It is he that proposes his new, and intriguing, 'contact' theory.Examining the evidence together, it is the fallen photographer's own work that seems to provide the clues which point toward the shadowy world of espionage that Sherlock's brother, Mycroft, inhabits. Deduction, a none too elegant disguise and splendid deception leads to a final denouement. Here, Watson stands alone and unarmed, facing a ruthless killer and is only a hair trigger away from certain death.