American rockets disappear with no explanation, each reporting a mysterious asteroid moments before vanishing. Captain Frank Chapman, sent to find the missing astronauts, loses control of his ship and crashes on the planetoid. When he recovers from the impact he discovers he has shrunk to the size of an insect. The asteroid turns out to be populated by a race of miniature people, the Rehtons, who enslave the captain in order to protect their secret. He becomes entangled in the struggle against the Solarites, inhuman creatures intent on destroying the Rehton civilization. As the alien assaults intensify, Chapman is torn between his love for a beautiful space woman and his desire to return to Earth. During a final spectacular battle with an escaped Solaritemonster, the captain makes a noble sacrifice for the good of both worlds.