The heroine had little time for romancing newspaper reporter Walter Jameson, what with Doctor X, alias Marcus Del Mar, threatening American democracy in general and master detective Craig Kennedy's designs for a new torpedo in particular. Whenever Doctor X has Elaine or Jameson in his grasp, they are inevitably saved in the nick of time by a mystery figure garbed in black.
| Actor | Role |
|---|---|
 Pearl WhiteElaine Dodge | Elaine Dodge |
 Creighton HaleWalter Jameson | Walter Jameson |
 Lionel BarrymoreMarcus Del Mar / Mr. X | Marcus Del Mar / Mr. X |
 Arnold DalyDetective Craig Kennedy | Detective Craig Kennedy |
 Warner OlandNot listed | Not listed |
| BBessie WhartonAunt Josephine | Aunt Josephine |
 George B. SeitzNot listed | Not listed |
| BBetty BordenNot listed | Not listed |
| HHoward CodyNot listed | Not listed |
 Paul EvertonNot listed | Not listed |
| RRobin H. TownleyNot listed | Not listed |
 Louis WolheimNot listed | Not listed |