Roy Thinnes and Ian Hendry star in this classic sci-fi directed by Robert Parrish. When a previously unseen planet is discovered on the opposite side of the sun, a European space agency hurriedly dispatches a spaceship to investigate. But when astronauts Colonel Glenn Ross (Thinnes) and John Kane (Hendry) are forced to crash-land, their dazed condition leads them to believe they're back on Earth. It's not long, however, until they both discover the shocking truth: the undiscovered planet is actually a doppelganger of the Earth, similar in every respect, but a mirror-image.