Chandu consults his crystal ball and sees that Nadji, Princess of Egypt, is in danger. She is about to be sacrificed by the black magic cult of Ubasti. Headed for the magic island of Lemuria, he is shipwrecked , washed ashore and captured. He becomes invisible, escapes and after numerous detours is able to rescue the princess.
| Actor | Role |
|---|---|
 Bela LugosiFrank Chandler (Chandu) | Frank Chandler (Chandu) |
 Maria AlbaNadji - Princess of Egypt | Nadji - Princess of Egypt |
 Murdock MacQuarrieThe Supreme Voice of Ubasti [Chs. 4-12] | The Supreme Voice of Ubasti [Chs. 4-12] |
 Clara Kimball YoungDorothy Regent | Dorothy Regent |
 Dean BentonBob Regent (as Deane Benton) | Bob Regent (as Deane Benton) |
| PPhyllis LudwigBetty Regent | Betty Regent |
 Lucien PrivalVindhyan, High Priest [Chs. 1-4] | Vindhyan, High Priest [Chs. 1-4] |
| CCyril ArmbristerHenchman Sutra [Chs.1-4] | Henchman Sutra [Chs.1-4] |
 Wilfred LucasCapt. Wilson [Chs. 4-12] | Capt. Wilson [Chs. 4-12] |
 Josef SwickardTyba, The White Magician [Chs. 8-12] | Tyba, The White Magician [Chs. 8-12] |
 Baby PeggyJudy Allen | Judy Allen |
 Dick BotillerMorta | Morta |
 Iron Eyes CodyCat Man | Cat Man |
 Louise EmmonsSisaba | Sisaba |
 John InceMr. James | Mr. James |
 Isabel La MalMrs. James | Mrs. James |
 Bryant WashburnPrince Andra | Prince Andra |
 J.J. ClarkVitras | Vitras |