IMDb 1 hour and 12 minutes (it seemed longer), rated 6.3 by 390 cinematizens.
That Hammer master of horror, Peter Cushing returns to Holmes twenty-seven years after he last donned the deerstalker in The Hound of the Baskervilles (1959) with John Mills (between the forest sideburns), the eternal Scotsman Gordon Jackson, a miscast Ann Baxter, a catatonic Ray Milland straight from Madame Tussaud’s, and Anton Diffring, as always the villain, in a 1913 London when war clouds gather.
Dead men without a mark start popping out the sewers. Taking Scotland Yard literally, Scotsman Gordo drags the scent across Holmes’s nose and stands back. The action is, well, by the numbers with a red whale, rather than a red herring, a gratuitous appearance of The Woman played by the dowager Baxter. There is some verbal sparing with The Woman, and one nice action scene when Watson dispatches a hooligan very economically on a moving train. Holmes’s major insight is that someone is lying.
Spoiler. The Aryan Anton, despite innocent appearances, has secretly been making poison gas down below so that when the war begins he can release it into the town gas that illuminated London. The dead men were production accidents.
The print I found on You Tube was terrible and that may partly explain why I found it boring.