 | Jack Mulhall | ... | Craig Kennedy |
 | Rex Lease | ... | Walter Jameson |
 | Mae Busch | ... | Mrs. Paul Gironda |
 | Ruth Mix | ... | Shirley McMillan |
 | William Farnum | ... | Gordon Gaunt |
 | Marion Shilling | ... | Verna Gironda |
 | Bryant Washburn | ... | Denton |
 | Robert Frazer | ... | Dr. Paul Gironda [Chs.1,4,8,13-15] |
 | Gaston Glass | ... | Louis Bouchard |
 | Mahlon Hamilton | ... | Montgomery [Chs.1,2,5,6] |
 | Robert Walker | ... | Mitchell |
 | Yakima Canutt | ... | Number Eight |
 | Joseph W. Girard | ... | Cromwell [Chs.1-3,6,7,15] |
 | Frank Leigh | ... | Wickham |
 | Jon Hall | ... | Hobart (as Charles Locher) |
 | Franklyn Farnum | ... | Nicky |
 | Knute Erickson | ... | Capt. Hansen [Chs.3, 11-14] (as Knute Ericksen) |
| rest of cast listed alphabetically: |
 | Richard Alexander | ... | First Mate Olaf [Chs.11-12,14] (uncredited) |
 | George Allen | ... | Sailor (uncredited) |
 | Eugene Burr | ... | Board Director [Chs. 1-2, 15] (uncredited) |
 | Roy Cardona | ... | O'Hara - Henchman Number Two (uncredited) |
 | John Cowell | ... | Officer Bill [Ch.1] (uncredited) |
 | William Desmond | ... | Bartender Steve [Chs.5,8,10-12,14] (uncredited) |
 | Earl Douglas | ... | Wilson - Henchman Number Four / Carlos Gaston [Ch. 9] (uncredited) |
 | John Elliott | ... | Attorney Arthur J. White (uncredited) |
 | Art Felix | ... | Riley - Sailor Guard [Chs. 11-12] (uncredited) |
 | Gordon Griffith | ... | Blackie Humphries, alias Hamik [Chs.3,5,7,10,11] (uncredited) |
 | Ethel Grove | ... | Margaret, the Maid [Chs.1,5-7,10] (uncredited) |
 | Henry Hall | ... | Warden [Ch.1] (uncredited) |
 | Art Howard | ... | Board Director [Chs. 1-2, 15] (uncredited) |
 | Bert Howard | ... | Board Director [Chs. 1-2, 15] (uncredited) |
 | Reed Howes | ... | Private Detective Sullivan (uncredited) |
 | John Ince | ... | Police Officer Regan [Ch.1] (uncredited) |
 | Willard Kent | ... | Jewet, Board Director [Chs. 1-2, 15] (uncredited) |
 | Bob Kortman | ... | Henchman Number Six - aka Spike Harvey (uncredited) |
 | Tom London | ... | Nellie D Sailor [Chs. 1,11-14] (uncredited) |
 | Allen Mathews | ... | Bus Driver (uncredited) |
 | Carl Mathews | ... | Henchman [Chs. 3-8] / Sailor Bar Brawler (uncredited) |
 | Bull Montana | ... | Slug, Nellie D Sailor [Chs. 2, 11-14] (uncredited) |
 | Milburn Morante | ... | Marty, the Delivery Man [Chs.2,6-8] (uncredited) |
 | George Morrell | ... | Jenkins, Craig's Butler (uncredited) |
 | Artemus Nigolian | ... | Denton's Maid [Ch.14] (uncredited) |
 | Eddie Parker | ... | Henchman (uncredited) |
 | Gil Patric | ... | Board Director [Chs. 1-2, 15] (uncredited) |
 | Pascale Perry | ... | Policeman (uncredited) |
 | 'Snub' Pollard | ... | Waiter [Chs.1,11-12] (uncredited) |
 | Robert Russell | ... | Trustee [Ch.1] (uncredited) |
 | Vera Steadman | ... | Miss Dillon [Chs. 1, 6, 10, 14] (uncredited) |
 | Ken Strickfaden | ... | Strick - Lab Assistant (uncredited) |

| Slim Whitaker | ... | Nellie D Sailor [Chs. 2, 11-14] (uncredited) |
 | Roger Williams | ... | Gallagher, alias Aji [Chs.3,5,10,11] (uncredited) |