 | Scott Kolk | ... | Agent Dexter (X-9) |
| Jean Rogers | ... | Shara Graustark |
| David Oliver | ... | Pidge |
| Monte Blue | ... | Baron Michael Karsten |
| Henry Brandon | ... | Blackstone |
| Larry J. Blake | ... | Chief FBI Agent Wheeler (as Larry Blake) |
| Henry Hunter | ... | FBI Agent Tommy Dawson (C-5) |
| George Shelley | ... | Henchman Packard |
| Lon Chaney Jr. | ... | Maroni (primary henchman) |
| Si Jenks | ... | 'Jolly Roger' ticket barker [Chs. 1, 4, 7-9] |
| Lynn Gilbert | ... | Rose, gang moll [Chs. 2, 6-7, 12] |
| Robert Dalton | ... | Thurston |
| Leonard Lord | ... | Ransom (dissident henchman) [Chs. 1-6] |
| Ben Hewlett | ... | Scarlett (primary henchman) (as Bentley Hewlett) |
| Bob Kortman | ... | 'Trader' Delaney [Chs. 7-9, 11-12] (as Robert Kortman) |
| rest of cast listed alphabetically: |
| Thomas Carr | ... | FBI Agent Tracy (phoney newsboy) [Chs. 3, 5, 7, 8] (uncredited) |
| Jack Cheatham | ... | Henchman Sebastian [Chs. 8, 11-12] (uncredited) |
| Al Ferguson | ... | FBI Agent Dyer [Chs. 1, 7] (uncredited) |
| Max Hoffman Jr. | ... | Henchman Marker [Chs. 1-2] (uncredited) |
| George Magrill | ... | Freighter crewman [Chs. 9-10] (uncredited) |
| Charles Murphy | ... | Jolly Roger Ticket-taker (uncredited) |
| Eddie Parker | ... | Marine Guard [Ch. 1] / FBI Agent Crain [Chs. 6-8, 11-12] / Henchman [Chs. 11-12] (uncredited) |
| Edward Peil Sr. | ... | The Fence [Chs. 11-12] (uncredited) |
| Elliott Rothe | ... | Agent Jimmie Tilden [Ch. 1] (uncredited) |
| William Royle | ... | FBI Agent Dunn [Chs. 1, 2, 5-7, 10, 12] (uncredited) |
| Tom Steele | ... | Policeman [Chs. 1-2] / Marine Guard [Ch. 1] / Henchman [Chs. 2, 5, 10] / FBI Agent [Chs. 7-8, 11] / 'Jolly Roger' sailor [Chs. 9, 11-12] (uncredited) |
| Charles Sullivan | ... | Truck Driver [Ch. 4] (uncredited) |
| Eddy Waller | ... | Lawyer Carp [Chs. 2, 12] (uncredited) |
