Atomic scientist/pilot Doug Martin is missing after his plane crashes on an reconnaissance mission after a nuclear test. Miraculously appearing unhurt at the base later, he is given sodium amethol, but authorities are skeptical of his story that he was captured by aliens determined to conquer the Earth with giant monsters and insects. Martin vows to use existing technology to destroy them.

Scientists investigate a huge meteor that crashes into the ocean off Mexico, and encounter a skyscraper-tall, mobile machine which is designed to syphon energy from earth, including any energy directed at it in an effort to destroy it.

A group of extra-terrestrials determined to take over the earth and make it their new home, station themselves in a canyon and set about their task.