A Martian invader crashes his spaceship conveniently close to the workshop of a scientist who is developing an interplanetary craft. If the extraterrestrial Purple Monster can complete the rocket ship and return to Mars, he will be able to start a full-scale invasion of Earth. Good thing Craig Foster sets out to thwart the Monster's mission!
| Actor | Role |
|---|---|
 Roy BarcroftThe Purple Monster | The Purple Monster |
 Dennis MooreCraig Foster | Craig Foster |
 Linda StirlingSheila Layton | Sheila Layton |
 James CravenDr. Cyrus Layton | Dr. Cyrus Layton |
 Bud GearyHodge Garrett | Hodge Garrett |
| MMary MooreMarcia | Marcia |
 John DavidsonEmperor of Mars | Emperor of Mars |
| JJoe WhiteheadCarl Stewart | Carl Stewart |
 Emmett VoganSaunders | Saunders |
 George M. CarletonDr. Paul Meredith | Dr. Paul Meredith |
 Kenne DuncanCharles Mitchell | Charles Mitchell |
| RRosemonde JamesHelen | Helen |
 Monte HaleDr. Harvey | Dr. Harvey |