Holmes has been approached by a doctor, Percy Trevelyan. Only recently licensed and low on funds, he had accepted a business offer from a Mr. Blessington, a man with “thousands” to invest, who set Trevelyan up in a practice, in return for lodgings, a profit share, and the supervision of his heart condition.

Trevelyan consults Holmes because his “resident patient” has recently become inexplicably jittery. After a burglary nearby, Blessington insisted they increase the house’s security, and then, a few days ago, an odd incident had left him in tears. Trevelyan had received a new patient—an elderly Russian count with catalepsy. His son had brought him, and remained in the waiting room. During the examination, the patient had a fit, so Trevelyan left to get medicine—only to discover both men had vanished when he returned.

The next day the men came back to resume the consultation, apologizing for their abrupt exit. Later, when Blessington returned from a walk, he claimed an intruder had been in his room. A footprint on the carpet confirmed this, and Trevelyan realized that the count’s son must have slipped upstairs from the waiting room. The incident had left Blessington crying and almost incoherent with fear.

Holmes accompanies Trevelyan to the practice. He is sure that the men were after Blessington himself, rather than anything in the room, but Blessington insists he has no idea who the intruders are. Holmes leaves, disgusted, saying that he cannot help if he refuses to tell the truth.

The next day, Blessington’s corpse is found hanging from a noose hitched up in his room. In spite of the police’s initial verdict of suicide, Holmes’s deductions show that this is murder. Four cigar ends in the fireplace, as well as footmarks on the stairs, show that three people had surreptitiously made their way upstairs during the night. A screwdriver and screws left in the room suggest that the three felons had planned to build a set of gallows, before deciding to make use of a light fixture to “execute” Blessington.

Investigations reveal that the trio were in the notorious “Worthingdon bank gang”—a group of murderous robbers. Blessington (whose real name is Sutton) was a key member, but when the gang was caught, he had turned informer and escaped prison. His sordid death was a vengeance 15 years in the making: on their release, the men had hunted him down, two of them posing as the Russian count and his son. The three assailants are not caught at the time, but Watson reports at the end of the tale that they were later aboard an “ill-fated steamer” that vanished at sea.

Cavendish Square, close to Harley Street, was—and still is—a well-known site for medical practices. Blessington’s patronage enables Percy Trevelyan to practice in the vicinity.

Trevelyan shares some similarities with his creator. Conan Doyle had also struggled with a “want of capital” when trying to establish a medical practice. Trevelyan has the look of “an artist rather than of a surgeon,” and has written a monograph on obscure nervous lesions—the subject of Conan Doyle’s own university thesis. And both the author and his character are supported by the proceeds of crime, whether Blessington’s stolen loot or Holmes’s commercial success.