After dark, four total strangers (a reporter, an opera singer, a doctor and a small boy) meet in a park. Each of them is there because they'd received a mysterious note urging their that they attend. Astroboy arrives explaining that he sent the notes and each of them are not on Earth at all, but were abducted by aliens and are prisoners on Planet X. They are to escape in a rocket Astro has hidden in the park. Soon after lift-off, they are pursued by flying space mines which form an energy web after exploding, holding the rocket captive.