Bennett notes particularly strange incidents: one, in which he saw the professor crawling along the hall on his hands and feet and his master swore him off; and another, witnessed by Edith Presbury, who saw her father at two o'clock in the morning at her bedroom window on the second floor.

Holmes forms a theory that every 9 days Professor Presbury takes some drug which causes the odd behaviour, having become addicted in Prague, and is supplied by Dorak in London.

It contained a drug, as Holmes expected, but also a letter from a man named Lowenstein, who Watson reveals to be a notorious quack.

David Stuart Davies, who has written an afterword for the Case-Book, comments that this story "veers towards risible science fiction".

Ancient philosophy scholar Jonathan Barnes writes of encountering the story as a child and finding it "one of the richest and most singular investigations of Holmes's long career – an opinion which I have had no reason to change ... Revisited in adulthood, the story reveals itself as a sour parable about the endurance of lust, a lurid treatment of the question that is put to Falstaff as Doll Tearsheet fidgets on his knee: 'Is it not strange that desire should so many years outlive performance?'.

Yet, curiously, the feeling persists that there is something in the narrative – hidden, submerged – which the reader is not permitted to comprehend but which forms the source of its power.

"[2] "The Adventure of the Creeping Man" was published in the UK in The Strand Magazine in March 1923, and in the US in Hearst's International in the same month.

[6] The story was adapted by Edith Meiser as an episode of the American radio series The Adventures of Sherlock Holmes.

[7] Meiser also adapted the story for the American radio series The New Adventures of Sherlock Holmes as an episode which aired on 27 November 1939 (as "The Mystery of the Creeping Man").

[12] The adaptation is relatively faithful to the plot, but includes a subplot involving Inspector Lestrade investigating the thefts of various primates from London's zoos: these are later revealed by Holmes to be the sources from which the serum is obtained.

[13] Lowenstein's development of a "rejuvenation serum" derived from monkeys parallels actual treatments popularised in the early twentieth century, notably those of the Russian-born surgeon Serge Voronoff, who had experimented with injections of extracts from animal glands; in the 1920s, he popularised the transplantation into humans of tissue from monkey testicles.