At an officers club Anchorage Alaska, Ned "Scotty" Scott (Douglas Spencer) meets with a group of air force officers playing cards. Amid the small talk Scott tells the men that he is a reporter looking for a story. One of the officers admits that a large number of scientists are at the North Pole. Scott takes an interest on the matter but nothing more is said.
Captain Patrick Hendry (Kenneth Tobey) is paged to General Forgety's quarters. Forgety explains that a strange aircraft has been found at the pole, Hendry is put in charge of the recovery mission. Remembering the earlier conversation he asks if Scott can fly up with the recovery team.
Arriving at the pole they meet with the scientists who are excited about the potential of the find. Hendry catches up with a science assistant Nikki Nicholson (Margaret Sheridan). It is clear from their encounter they have an extensive social past.
Nikki introduces Hendry to Dr. Arthur Carrington (Robert Cornthwaite) leader of the scientist based at the north pole. Carrington tells Hendry the crashed aircraft is located about 48 miles from the base. When the plane crashed instruments recorded an explosion and magnetic flux disturbance that indicates the plane weighs approximately 20,000 tons.
Hendry suggests that, given the recorded weight of the vessel, they must be dealing with a meteor. Carrington, however, shows him a number of radar tracks that show the object change course and speed a number of times before crashing.
The expedition flies to the location to begin to unravel the mystery, as they approach the reported location the aircrafts compass begins to malfunction then Geiger counters begin registering erratic levels of radiation. Finally they see a tear dropped object partially buried in the snow.
Arriving at the actually crash site they realize whatever landed was so hot that it melted enough snow to sink down so that only a stabilizer fin is protruding from the ice. To establish the actual size of the craft the team slowly spreads out over the object. After a few minutes it becomes obvious the craft is circular. We finally got one yells a scientist, believing they have just located a UFO.
Thermite bombs are used to melt the ice around the craft, unfortunately something in the metal used to build the ship reacts to the thermite and the scientist look on in horror as the whole vehicle disintegrates destroying all evidence of the ship and its origins. A minute later, second object is found in the ice near the remains of the spaceship and on closer investigation they believe it may have been the pilot of the ship. Not willing to risk thermite's contamination, they cut the creature out of the ice and make plans to transport the complete block of ice back to base.
At the base, Hendry refuses to allow the scientists to defrost the block. After the destruction of the ship he doesn't intend to take any more chances He also has a concern about potential disease that may be carried by the creature, or what could happen once the creatures body came in contact with Earth's atmosphere.
To secure the block Hendry moves it to a storeroom then breaks the windows to stop any possibility of the ice melting. Hendry sets watches at 4 hour intervals. The first watch is stood by Lt. Ken "Mac" Macpherson (Robert Nichols). The base radioman, Corporal Barnes (William Self) reports that the weather has cut the base of from communication with the outside world. He cannot receive messages but thinks he might still be able to send.
Hendry gives him a report on the situation, as well as a request from the scientists to examine the creature. Later that night Barnes reports he got through and has received instructions. Scott is frustrated that someone in Washington has leaked the story, and although he is the only reporter at the base, no one can hear his story. General Fogerty has also forwarded Hendry's report to the highest levels of government, and is waiting for further instructions.
Everyone standing watch on the creature is becoming badly spooked. The ice block has become a little transparent and the creature's face can be seen. The eyes give the impression the creature is still alive, Hendry adjusts the watch from four to two hours.
The base settles in for the night and Nikki confides in Hendry that she is unsure about what to make out of the situation. She also compliments Hendry on his handling of the situation; she then offers to buy him a drink. They retire to her office and the obvious attraction begins to flower, ending in a steamy kiss and admission of mutual attraction.
Back at the storage room, Barnes has taken over the watch on the creature. Not thinking, he throws an electric blanket over the block of ice causing it to defrost unnoticed. Distracted by the novel he is reading, Barnes doesn't notice movement behind him before it is too late. Jumping to his feet he draws and fires his gun as he retreats from the storage room.
Barnes reports to Hendry and the scientists that the creature is alive and it chased him. Hendry and the group return to the room to find the hollowed out block of ice and creature is gone. Through a broken window they can hear a battle going on between the camp dogs and the creature. The men race to the aid of the dogs, but the creature escapes.
The scientists discover an arm of the creature torn off during the attack. The scientists begin investigating the arm. First they discover the arm is made of cretin and laced with barbs, they suspect this makes the creature amazingly strong. The arm also appears to have no nerves and the cellular structure is identical to vegetables.
Dr. Carrington, having found seed pods attached to the creature's arms, surmises that on its home planet, plants rather than animals evolved intelligence. As the debate continues the arm begins to move by itself. Carrington although surprised, thinks this is caused by various parts of the creature being able to become independent organisms.
Hendry is concerned the creature may re-enter the base. Everyone is armed with guns and axes and a search begins. At the greenhouse, Carrington notices something wrong but fails to report his suspicions to Hendry.
After the soldiers leave, Carrington points out to some of the scientist that a number of the most temperature sensitive plants have died, probably from exposure to cold air. Searching the room they discover the body of a dog, drained of blood.
The creature had been there and had fed on the dog. He asks the scientists to watch the room without telling Hendry.
Having swept the base, Hendry searches outside. On returning he is greeted by Dr. Chapman, who badly injured he explains the scientists have been attacked and killed in the greenhouse. Chapman adds that he saw bodies hanging from rafters and appeared bled dry of blood.
Hendry races to the greenhouse and is immediately attacked by the alien. Escaping Hendry closes the door then shores it up to stop the creature breaking into the rest of the base. Carrington quietly gathers the remaining scientists and explains the situation. The alien is intelligent and he believes the creature intends to kill everyone at the base. He then shows them an experiment he's set up.
Taking a number of seeds from the creatures arm, he's planted them and fed them a diet of blood. Within four hours the seeds had sprouted and were continuing to grow quickly. Using a stethoscope he believes he can hear the plants wailing like new born children looking for food.
Some of the scientists are repulsed by Carrington's actions and try to convince him to tell Hendry. He refuses believing only the scientists can save the situation.
Nikki finds Hendry and shows him Carrington's notes. Hendry realizes this explains a secondary issue they have had: to find the basic blood supply that is needed to treat Chapman for his injuries.
Hendry confronts Carrington, who refuses to buckle and stop the experiment. Hendry wants the plants destroyed and the creature trapped and destroyed in the greenhouse. A message from Fogerty interrupts the exchange, he has instructed all efforts must be made to keep the alien alive. Carrington sees this as validation for his actions.
Frustrated and deciding Fogerty is not in full understanding of what is happening at the base, Hendry decides to ignore the General's instructions. He gathers all the military personnel in the mess hall to consider options. They agree on an idea of dousing the creature with kerosene and lighting it, hopefully cooking the alien. Nikki points out one of the geiger counters has begun to react. It means the creature is on the move and if the readings are correct, heading for the mess hall.
Everyone scrambles to get ready as the alien bursts into the room. They successfully ignite the kerosene and set the Thing on fire, but the creature escapes back outside using the snow to douse the flames. Regrouping the men decide to repeat the attack, only this time using a lot more kerosene. Hendry suggests a different strategy, rather than burn the creature he wants to try electrocution.
The creature shows its intelligence by cutting the oil flow to the heating system. Hendry believes the creature is trying to set its own trap. Anyone who attempts to repair the oil line will be ambushed and killed
Hendry thinks if this fails the creature will next attack the power generators. As such he decides to lay his own trap at the generators and try the electrocution idea.
Frantic preparations ensure as the men build barricades to force the creature to approach from a specific direction. Almost as soon as they are finished one of the men reports movement near his barricade. The creature moves off and then begins attacking in the direction needed to trigger the trap.
Suddenly the lights go out and Nikki screams that Carrington has cut the power, Carrington is quickly overpowered and the all important power is restored.
Furious Carrington rushes towards the creature and tries to explain to it that humans are intelligent and that both species could learn from each other. The creature seems completely unimpressed with the encounter and swats Carrington away before once again advancing menacingly. Hendry sees his chance and springs the trap as electrical bolts hit the Thing. The creature struggles briefly before being reduced to a small pile of ash. Nothing is recognizable; nothing is left to show the threat from space ever existed.
A little later, the men are gathered and going over what's been accomplished. Carrington is alive but injured. The men report that all Carrington's notes have been destroyed along with the alien arm and all the seedlings.
With things settling down Nikki corners Hendry and discusses the possibility of taking their friendship a step further and would he consider settling down. He seems to suggest he might and they go to a corner to discuss their future.
The radio is now transmitting and receiving clearly, Scott takes the opportunity to send his story to the assembled newsmen back in Anchorage. After recapping events he ends his broadcast with a chilling note. "Watch the skies, everywhere, keep looking, and keep watching the skies."