It is an autumnal evening in the early 1880s, and Sherlock Holmes and Doctor Watson have just returned from an evening constitutional around central London. They find Dr Percy Trevelyan waiting for them with a strange story about his benefactor and resident patient, Mr Blessington. Having set Trevelyan up in a prestigious practice in Brook Street, the well-regulated Blessington has recently become a nervous wreck, a prey to exaggerated fears of burglary. And now there is evidence that the inner sanctum of his living quarters has been visited by strangers whilst he was absent. Thus Trevelyan has been sent to lay the matter before Sherlock Holmes. Perhaps the key to the mystery could lie with the recent visit of two Russian noblemen to Brook Street…