Since London awaits each installment of his Sherlock Holmes stories with bated breath, Arthur Conan Doyle would seem to be a lucky man. But he also has a bit of a problem. His publisher George Lippincott, on a trip to Edinburgh, has turned up dead. And not merely dead - murdered in a lurid scene drawn from one of Doyle's as yet unpublished stories. When Doyle appeals to the Scotland Yard forensics team for help, Tom and Davy, both avid Sherlockians, jump at the chance, but the unit leader, Detective Trevor Welles, is not so sure. He finds Doyle and his brilliant fictional sleuth ludicrous and suspects the "murder" is little more than a publicity stunt staged by an arrogant author and his greedy publisher. It is only when Emma Kelly, another member of the team and the object of Trevor's affection, receives a valuable pearl from an anonymous source - the opening scene of The Sign of the Four - that Trevor agrees they must indeed take Scotland Yard to Scotland. Edinburgh is a city abuzz with a strange series of crimes involving gypsies, cobras, roman soldiers, poison darts, and any number of improbable events, all drawn from the pages of Doyle. As the team scrambles to contain the mayhem, they learn that their chief suspects, a duo of men who always seem to be close to the action, in fact represent another division of Scotland Yard, one of the force's first undercover units. These men, especially the infuriatingly suave Richard Wright, aren't afraid to bend the rules or pocket the occasional bribe, and, between his young assistants' admiration for Doyle and Emma's attraction to Wright, Trevor feels as if he is losing control over his team, if not his whole life. Can the killer outthink two groups of Scotland Yard detectives and Arthur Conan Doyle himself? The answer lies at the top of a waterfall, where it takes total darkness to bring the truth to light.