From a lonely castle set in the foggy moors of a remote Scottish isle, astronomy Professor Eliot and his pretty daughter Enid discover a planet approaching Earth from the depths of space.

    The professor dubs the rogue world Planet X, and handsome reporter John Lawrence turns up looking for the story of a lifetime. As Planet X draws closer and closer to Earth, Lawrence and Enid (played by Sally Field's mom, Margaret Field) find an oddly-shaped alien spacecraft while walking off their dinner one evening. And in a classic scene where Enid peers into the spaceship's window, they see there is a little "man" inside!

    Professor Eliot and Lawrence seem to befriend the alien, who can only communicate through musical melodies, and take him back to the castle. But once there, the professor's nefarious assistant Mears tries to beat some secrets out of the man from Planet X. The alien responds by returning to his spaceship and fortifying his landing site. He also takes hostages, including feisty Enid, with a ray gun that turns earthlngs into zombie-like slaves.

    At that point, Lawrence figures out that the alien is really the advance scout for a massive invasion. The intrepid reporter has to convince the authorities to use military force against the alien before Planet X draws any closer.