The movie begins with a spaceship traveling to the planet Altair IV in search of a survey team that had dissapeared nearly 20 years ago. The captain discovers the planet is inhabitated by a lone scientist, his robot Robby, and his innocent daughter. At first the scenery is wonderous and the time spent on the planet seem best suited as a time of rest and relaxation The captain continues to try to uncover what happened to the survey team from earlier. As he does this. strange things begin to happen. The ships crewman start being hurt and killed by a mysterious force.

The captain of the ship finds great allure in the scientist's daugher on this planet. This girl has never seen men before except for her own father. She is innocent and doesen't even know what a kiss is. The ship's captain finds this intriguing and romances her in his own way but constantly is suspicious of her father, the scientist. The scientist reveals that once a great alien civilization existed on the planet known as the krell. How they died off remains a mystery.

Finally the captain discovers the truth of this planet. The scientist has harnested a means of thought amplication from the krell. He uses a head device which can manifest dreams and ideas into reality. Simply put what you wish for will come true. This would seem to be the greatest gift in the world. But even a man of science has to discover painfully that its hard to control one's wishes. The subconcious mind and our dreams desire things that we would reject logically on the surface. Unfettered and unrestricted thoughts manifest monsters and death. These thoughts kill off the captain's crew and threaten to kill everything which remains on the planet. This technology in fact was what killed of an entire race of aliens, the Krell.

The movie is most famous for its robot Robby which is quite similar to the Lost in Space TV robot which came later. The movie featured futuristic laser weapons, and costumes and presents a true tale of the the dangers of the subconcious mind amidst a science fiction setting. The essence of this story was recreated in the more recent Dustin Hoffman movie sphere.