The story is about a spacecraft sent to learn what exactly happened to a previous spacecraft and its' crew, which had been deployed many years prior, and has since not been heard from in some time. This current mission is under the command of Commander John J. Adams (Nielsen), and soon find themselves on approach to the destination planet of the now lost ship. On their arrival, they get an ominous message, from the planet, issued by a member of the original crew, Dr. Edward Morbius (Pidgeon). Despite his warnings, they land and are soon met by a robot named Robby, who escorts them to Morbius' rather posh abode. Here we learn all the members of that fated crew have been killed off, except for Morbius and his daughter (whom Morbius had when he procreated with another member of the original crew), Altaira (Francis), by some unseen, yet completely nasty, force, to which Morbius and his daughter seem immune. Not expecting to find any survivors, Commander Adams now has to change his plans to include trying to contact his superiors and receive further instructions on how to proceed, despite Morbuis' protests that they should leave as soon as possible, leaving him and his daughter behind so that he may continue his research. What is his research? Well, it seems that many hundreds of thousands of years ago, the planet was inhabited by a highly advanced race of being called the Krell, who mysteriously vanished seemingly overnight in comparison to their collective power, intelligence and abilities, and while their cities have long since gone, a great deal of their technology survived underneath the ground, and Morbius has managed to gain some understanding of these beings, even being able to pry bits of information and such in the 20 odd years that he's been here. This amazing discovery is certainly worth writing home about, and so Commander Adams begins having the men disassemble the ship to create a device powerful enough to send a message back to his superiors, and in the meantime, starts making time with Morbius' daughter, who's never seen a man outside of her father, and is uneducated in the ways of woo. Things seem to be progressing until an unseen late night attack on the ship damages some crucial elements needed for communication, so an electrified perimeter is set up to prevent the approach of any more unannounced and unwelcome visitors. We soon find out the fence works, as a huge beastie, normally invisible, now highlighted by the electrical current, tries to attack the ship, killing a few defenders. What exactly is the nature of this beast? Is it somehow connected to the Krell? Does Morbius know more than he's letting on? Will any get off this planet alive? What the heck were these Krell up to anyway?