One of several titles in the Sherlock Holmes series whose original copyrights were apparently not renewed and have thereby fallen into public domain; as a result, seriously inferior copies are presently being offered by a number of VHS and DVD dealers who do not have access to original studio masters.
Although credited as an adaptation of Sir Arthur Conan Doyle's short story "The Adventure of the Dancing Men", the plot is an original story based on historical events which happened after Doyle's death. The only resemblance to the credited story is a cameo by the "secret code" of stick figure drawings. There is another moment taken from Doyle's "Sign of Four": the trail of luminous paint is confused when luminous paint is picked up by wheels of another vehicle at a crossroads.
Moriarty taunts Holmes by saying "The needle to the last, eh, Holmes?" Possibly a reference to Sherlock's cocaine habit, an important character element from the books. This could not be depicted openly in this series, due to film taboos of the time. Or maybe this line simply means that Holmes is a "needle" in Moriarty's side.
A modern source lists Philip Van Zandt as Kurt and includes Henry Daniell in the cast as well. However, the role of Kurt is played by Harry Woods and neither Van Zandt nor Daniell appear in the film at all. The unidentified actor mistaken for Daniell plays a Scotland Yard detective slowly driving the police vehicle following the trail of paint, toward the climax of the film. First seen in 3/4 profile leaning out the car window, he does seem to resemble Daniell. However, when he speaks the accompanying line "they fade out again sir" to Dennis Hoey (Insp. Lestrade), and subsequent lines, he clearly has a rather heavy *Brooklyn* accent, and seen in other shots during the scene does not in any way resemble Daniell, and the momentary appearance to the contrary is clearly an optical illusion.
During the sequence showing the trials of the new bomb-sight, several different types of aircraft are seen in the stock footage used. A Douglas A-20 (known in RAF service as the "Boston") takes off, then a Bristol Blenheim flies low past the camera, and finally a Vickers Wellington is seen for the rest of the sequence. The interior of the aircraft shown also appears to be a Wellington, recognisable by its unique framework of aluminium triangles.
One of the principal actors in this classic Sherlock Holmes film, the man who plays Sir Reginald Bailey, is actually named "Holmes" --- Holmes Herbert. Herbert also starred in several of the other S.H. films in the Basil Rathbone/Nigel Bruce series.