A brief establishing shot of Baker Street, with a street-cleaning cart passing by, is actually a piece of footage from The Private Life of Sherlock Holmes (1970).
Thorley Walters, who had played Dr. Watson in several different projects, replaced Trevor Howard as Major John Sholto, marking the final time Walters would play a character in the Sherlock Holmes canon on screen.
In the novel on which the movie is based, Holmes is indulging in his cocaine habit when Watson shows him the pocket watch. Here, he is conducting an experiment on tobacco smoke.
Ian Richardson later appeared in Murder Rooms: Mysteries of the Real Sherlock Holmes (2000) as Dr. Joseph Bell, the real-life inspiration for Holmes.
At the one-hour mark, Watson says, "Mrs. Morstan you're shivering from the cold". She replies, 'It's not the cold that makes me shiver, it's fear". This is originally a line from "Violet Smith" from the short story "The Solitary Cyclist" from "The Return of Sherlock Holmes" (1905).
