Claire Forrest seeks her kidnapped scientist father, hidden somewhere on Mystery Island. He is held and forced to work on diabolical inventions by Captain Mephisto, a costumed villain.
| Actor | Role |
|---|---|
 Richard BaileyLance Reardon | Lance Reardon |
 Linda StirlingClaire Forrest | Claire Forrest |
 Roy BarcroftCapt. Mephisto | Capt. Mephisto |
 Kenne DuncanSidney Brand | Sidney Brand |
 Forrest TaylorProf. William Forrest | Prof. William Forrest |
 Forbes MurrayProf. Harry Hargraves | Prof. Harry Hargraves |
 Jack IngramEdward Armstrong | Edward Armstrong |
 Harry StrangFrederick "Fred" Braley | Frederick "Fred" Braley |
 Ed CassidyPaul Melton | Paul Melton |
| FFrank AltenJohn Raymond | John Raymond |
 Lane ChandlerPolice Insp. Reed | Police Insp. Reed |
 Russ VincentRuga | Ruga |
 Dale Van SickelBarker / Ritter / Lewis / Frazier / Sardon | Barker / Ritter / Lewis / Frazier / Sardon |
| TTom SteeleLyons / Bailey | Lyons / Bailey |
| DDuke GreenSpencer Harvey | Spencer Harvey |