In the film's gripping opening, an alien spacecraft traverses the vastness of space before breaking through Earth's atmosphere and crash-landing near Antarctica. The circumstances of its arrival remain shrouded in mystery. As the harsh winter of 1982 unfolds, a helicopter is seen racing after a husky dog, where a frantic man aboard fires weapons in a desperate attempt to kill the animal. The terrified husky finds refuge at Outpost 31, an American research station bustling with a crew of twelve preparing for the winter months.
The helicopter, bearing Norwegian markings, lands abruptly, and the Americans watch in confusion as two men emerge, speaking in a panicked frenzy. When one accidentally pulls the pin on a grenade and kills the pilot, chaos ensues. In a desperate bid to protect his team, [Garry](wilford-brimley) (the camp leader) shoots one of the Norwegians, leaving the crew bewildered about the strangers' motives, particularly regarding the husky.
Determined to uncover the mystery, [MacReady](kurt-russell), the helicopter pilot, and [Copper](richard-masur), the team's doctor, venture to the Norwegian base, which lies in ruins. Amid the destruction, they discover evidence of terror: a large ice block containing a horrific, alien creature. They transport this gruesome find back to their own outpost for analysis, where biologist [Blair](wilford-brimley) examines the remains, only to find a normal internal anatomy hidden beneath its warped exterior.
That night, the newly arrived husky is placed in a kennel with the sled dogs, triggering a horrifying transformation as it reveals itself as a grotesque alien entity capable of gruesome attacks. [Clark](richard-masur), the dog handler, witnesses this chilling moment as the creature begins to slaughter the other dogs. MacReady responds promptly, prompting the camp to intervene with flamethrowers to eliminate the abomination.
As the team delves deeper into the investigations, they learn that the alien being can flawlessly mimic any life form it consumes, leading to paranoia and fear of infection among the crew. They aim to contain the creature’s remains while speculating on the drastic implications for humanity if it escapes and reproduces. A shocking discovery reveals that the Norwegians had unknowingly awakened the creature, setting off a deadly chain of events.
Days pass within the frozen desolation, filled with rising tension and distrust. MacReady organizes a blood test to identify any infected crew member, but suspicion and chaos unfold as team members begin to turn on each other. Efforts to maintain control fail, resulting in catastrophic consequences as infected individuals are revealed through violent confrontations and desperate attempts to survive.
In a series of harrowing events, the research team dwindles down to a few survivors, including MacReady, [Childs](keith-david), and [Garry](wilford-brimley). They initiate a final stand against the alien threat, which is now hidden among them, leading to an explosive climax when they realize they must destroy the base to eliminate the creature once and for all. In a desperate last resort, MacReady hurls a lit stick of dynamite at the monstrous alien form of Blair, triggering a massive explosion that engulfs the research station.
As the smoke clears, MacReady finds himself face-to-face with Childs amidst the ruins, both men suspecting the other of harboring the alien within. In an unsettling stalemate, they grapple with their distrust over swigs of whiskey, reaching a haunting conclusion: who among them remains human, and will they live to see another day? As the film fades to black, viewers are left in suspense, pondering the fate of humanity against the backdrop of a chilling Antarctic winter and the lurking terror that may still lie within.
