In a short opening sequence, a flying saucer enters the Earth’s atmosphere.

                    Antarctica, 1982. For a mysterious reason, two armed men are chasing a sled dog from a helicopter and try to shoot him. Soon they come across an American research facility, occupied by a dozen scientists. As the helicopter lands and the dog reaches the team, one of the Norwegian is accidentally blown away by the grenade he wanted to throw. The other one starts to shoot at them, one of whom sees no other solution but to shoot back at him, killing him.

                    Apart from the fact that they have not been able to reach anyone with their radio for the last few days, the Americans have followed a rather quiet routine until this incident. Shocked yet intrigued, MacReady and Doc decide to go and have a look at the Norwegian facility. Inside what remains of the burnt station, they find the body of a man who seemingly slashed his veins with a razor, along with a massive block of ice which used to shelter something –now gone. There is another dead body outside, burnt with kerosene, with impossible shapes.

                    The corpse is brought back to the American facility. The medical analysis reveals normal internal organs in spite of the severely disfigured face and the distressing angles of the arms and legs. The team does not know how to react and return to routine activities, but as soon as the fleeing dog is left in the kennel he goes through a horrible transformation, spitting acid at the other dogs while red tentacles and spider-like legs grow out from its back. The barking attracts everyone; they first stare in awe at the vision of the misshaped dog revealed to be inside of the now indescribable beast, and then shoot at it, with Childs finally burning it.

                    The looks of the new corpse on the medical table first leave Blair (and the audience) speechless, before he explains that this organism imitates other life forms perfectly, throwing doubt among the others, worried about who might have been exposed to the creature.

                    Thanks to some material brought back from the Norwegian facility, MacReady finds the place where the ice block was extracted –right next to the crashed, partially buried flying saucer. When he comes back, because the creature was not actually killed by the fire, one of the scientists gets infected and has to be burnt. The team gets even more agitated when Blair loses control of himself, destroying their chopper and radio equipment in order to prevent what he fears would become a global epidemic if the Thing came to leave the station, assimilating and replacing every human.

                    MacReady locks Blair away, but he agrees that they have to get rid of the threat before the arrival of the rescue team in a few months. Doc suggests a test requiring some uncontaminated blood in storage but it only results in more suspicion and fear, for the blood has been tampered with and nobody is sure about who could have gotten hold of the safe keys. Night falls, with panic and fear becoming more and more difficult to contain for some.

                    Shadows run outside and suspicious noises keep being heard. Even if nobody trusts anybody anymore, the group forms small teams in order to find and unveil the infected ones. MacReady’s leadership is questioned by Childs, but he gets a flamethrower and uses it against one of the Thing’s victims. He then comes up with the idea of testing whether the blood of each remaining person tries to protect itself from a burning copper wire, proving that he is indeed human –but also that the man he shot in self-defense a few minutes ago was not infected. One of the following samples flees from the wire, but the flamethrower malfunctions, and the carrier finds time to transform and infect another team member before being killed.

                    Childs is left in the main facility as the three other negatives go outside in order to check on Blair. They discover that he was attempting to build a small spacecraft under the shack he was locked in. Then all lights go off because of the generator being sabotaged, and they understand that the Thing’s plan is not to rejoin the outside world anymore, but to freeze until the rescue team comes to deliver it. They agree they have to track it down and destroy it before (likely) freezing to death themselves.

                    The three of them use explosives, blowing away room after room. In the generator room, the infected Blair traps Garry, then Nauls, leaving MacReady alone, only to be attacked by a monstrous, gigantic instance of the Thing. He manages to throw a stick of dynamite at it and escapes as the base explodes.

                    Exhausted and cold, he is found by Childs, who provides a vague explanation when asked about his late wandering. Acknowledging a most probable death in a few hours anyway, they share a bottle of scotch.