t an isolated American research station in Antarctica, the winter crew is shocked when a Norwegian helicopter arrives, frantically shooting at a runaway sled dog. The helicopter accidentally explodes, and the surviving Norwegian tries to gun down the dog before station commander Garry shoots him in self-defense. The Americans take the dog into their kennels, completely unaware of what it carries.
Helicopter pilot MacReady and Dr. Copper fly to the Norwegian outpost to investigate what went wrong. They discover a charred, smoking ruin filled with corpses, suicide scenes, and the burned, twisted remains of a malformed, two-faced humanoid creature. They bring the burned tissue back to Outpost 31 for an autopsy.
That night, the rescued dog morphs into a horrifying flesh-mass inside the kennel, attacking the sled dogs. MacReady burns it with a flamethrower, but the truth is out: this alien absorbs other living beings and imitates their shape and memories perfectly down to each cell. Senior biologist Blair runs a computer simulation and realizes that if this entity reaches civilization, humanity will fall within twenty-seven thousand hours.
Blair snaps, destroying the communications radio, wrecking the station vehicles, and slaughtering the remaining dogs to stop the infection from leaving the camp. The team locks Blair inside an outdoor tool shed. Suspicion spreads fast as the men discover someone has sabotaged their supply of stored medical blood, eliminating any quick diagnostic check.
MacReady steps up, knowing that each individual piece of the creature has its own independent survival instinct. He ties the remaining men to chairs and heats a copper wire over a blowtorch to test blood samples taken from each person. When Palmer's blood shrieks and jumps away from the hot wire, the alien bursts into the open. MacReady destroys it with dynamite and a flamethrower.
The survivors head down to Blair's shed, only to find he has excavated a secret tunnel and built a small escape craft from salvaged parts. The creature cuts the station generators, leaving the remaining crew to freeze in the dark. Deciding that neither they nor the creature can leave alive, MacReady, Childs, Garry, and Nauls rig the entire facility with explosives. A giant Blair-Thing erupts from the ground, killing Garry, while Nauls disappears into the darkness. MacReady hurls a stick of dynamite directly into the monstrosity, blowing Outpost 31 to pieces.
