- Bela Lugosi
- Prof. Adam Anton Strang
- Viva Tattersall
- Vera Strang
- Malcolm McGregor
- Jack Foster
- Henry B. Walthall
- J.D. Bradley - Company President
- Robert Warwick
- Detective Robert Raymond
- Ethel Clayton
- The Countess Helen [Chs. 5-8]
- Roy D'Arcy
- Prof. Alexis Steinbeck
- Karl Dane
- Sparks - Dispatcher
- Lloyd Whitlock
- Young - Henchman #3
- Bob Kortman
- Jasper Slade - The Convict
- Lafe McKee
- D.W. Jerome - Company Vice President
- Lionel Backus
- W.B. Jarvis [Chs. 3-6, 12]
- Yakima Canutt
- Detective [Ch. 12]
- Kernan Cripps
- Murphy - Driver [Chs. 1, 8]
- Gordon De Main
- Detective [Chs. 1, 5-8]
- William Desmond
- Empire Transport Co. driver
- Norman Feusier
- Deane [Ch. 10]
- Robert Frazer
- Official
- George J. Lewis
- Bud Foster [Ch.1, 8]
- Tom London
- Dupont - Henchman #5 [Chs. 1-8,12]
- George Magrill
- Mitchell - Henchman #2 [Ch. 2]
- George Morrell
- Empire Warehouse Worker
- Eddie Parker
- Gus - Driver Bud's Partner - [Ch. 1, 3]
- Jack Perrin
- Williams - Henchman #1 [Ch. 3]
- Max Wagner
- Kruger - Henchman #6 [Ch. 1]
