A card cheat is threatened with exposure into joining a criminal enterprise that Sherlock Holmes believes is controlled by Professor Moriarity.
| Actor | Role |
|---|---|
 Arthur WontnerSherlock Holmes | Sherlock Holmes |
 Ian FlemingDr. John Watson | Dr. John Watson |
 Minnie RaynerMrs. Hudson | Mrs. Hudson |
 Leslie PerrinsRonald Adair | Ronald Adair |
 Jane WelshKathleen Adair | Kathleen Adair |
 Norman McKinnelProf. Robert Moriarty / Col. Henslowe | Prof. Robert Moriarty / Col. Henslowe |
| WWilliam FazanThomas Fisher | Thomas Fisher |
| SSydney KingTony Rutherford | Tony Rutherford |
| PPhilip HewlandInspector Lestrade | Inspector Lestrade |
| GGordon BeggMarston, the butler | Marston, the butler |
| LLouis GoodrichColonel Sebastian Moran | Colonel Sebastian Moran |
 Harry TerryNo. 16 | No. 16 |
 Charles PatonJ.J. Godfrey | J.J. Godfrey |