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.
Lance Reardon
Claire Forrest
Capt. Mephisto
Sidney Brand
Prof. William Forrest
Prof. Harry Hargraves
Edward Armstrong
Frederick "Fred" Braley
Paul Melton
John Raymond
Police Insp. Reed
Ruga
Barker / Ritter / Lewis / Frazier / Sardon
Lyons / Bailey
Spencer Harvey
