A test pilot is missing and a search party is sent out in the jungles of Mexico; however, while searching they uncover a monster in the jungle who became this way due to a dose of radioactivity.
| Actor | Role |
|---|---|
 James CraigRuss Bradford | Russ Bradford |
 Gloria TalbottSusan Winter | Susan Winter |
 Lon Chaney Jr.Martin 'Marty' Melville | Martin 'Marty' Melville |
 Tom DrakeLee Brand | Lee Brand |
 Duncan 'Dean' ParkinThe Cyclops | The Cyclops |
 Vicente PadulaThe Governor | The Governor |
| MMarlene KlossThe Salesgirl | The Salesgirl |
| MManuel LópezThe Policeman | The Policeman |