Dressed to Kill, 1946 starring Basil Rathbone as Sherlock Holmes

Dressed to Kill, released in 1946, also known as Prelude to Murder (working title) and Sherlock Holmes and the Secret Code in the United Kingdom, is the last of fourteen films starring Basil Rathbone as Sherlock Holmes and Nigel Bruce as Doctor Watson.
Plot:

A convicted thief in Dartmoor prison (played by an uncredited Cyril Delevanti) hides the location of stolen Bank of England printing plates inside three music boxes (each of which plays a subtly different version of “The Swagman”). The boxes are sold at a local auction house.

A criminal gang’s brains belong to a darkly beautiful, ruthless woman, who is also a “consummate actress”, as Holmes learns. She disguises herself as a charwoman and speaking Cockney, insults and berates both Holmes and Watson, whom she pretends not to recognize, and leaves with a music box right under their noses. Holmes must recover the last music box to crack the secret code contained in the tune before it is too late.
Cast:

Basil Rathbone as Sherlock Holmes
Nigel Bruce as Dr. John H. Watson
Patricia Morison as Hilda Courtney/Charwoman
Edmund Breon as “Stinky” Emery (as Edmond Breon)
Frederick Worlock as Colonel Cavanaugh (as Frederic Worlock)
Carl Harbord as Inspector Hopkins
Patricia Cameron as Evelyn Clifford
Holmes Herbert as Ebenezer Crabtree
Harry Cording as Hamid
Mary Gordon as Mrs. Hudson
Ian Wolfe as Commissioner of Scotland Yard
Anita Sharp-Bolster as the Schoolteacher on a Museum Tour