Basil Rathbone as Sherlock Holmes

Nigel Bruce as Doctor Watson

Marjorie Lord as Nancy Partridge

Henry Daniell as William Easter

George Zucco as Heinrich Hinckel aka Richard Stanley

John Archer as Naval Lt. Pete Merriam

Gavin Muir as Mr. Lang, government agent

Edmund MacDonald as Detective Lt. Grogan

Don Terry as Howe

Mary Gordon as Mrs. Hudson

Bradley Page as Cady

Clarence Muse as George

Mary Forbes as Mrs. Pettibone

Holmes Herbert as Mr. Ahrens

Thurston Hall as Sen. Henry Babcock

Ian Wolfe as Antiques Store Sales Clerk

John Burton as Army Inspector (uncredited)

Gerald Hamer as Alfred Pettibone

Gilbert Emery as Sir Henry Marchmont (uncredited)

Margaret Seddon as Miss Pringle (uncredited)

Mary Field as Party Pianist (uncredited)

Colin Kenny as Hotel Doorman (uncredited)

Caroline Frances Cooke as Mrs. Ruxton