Who Goes There? recap

An Antarctic expedition recovers a frozen extraterrestrial from the ice and thaws it for study. The creature escapes and reveals an ability to absorb living beings and reproduce them perfectly, including their memories and behavior. After it attacks the sled dogs, the men destroy the visible body, but biologist Blair calculates that any copied animal or person could spread the organism until it replaces all other life. He destroys the station's aircraft and radio to prevent escape and is confined. Suspicion then turns inward because no one can prove who remains human. McReady recognizes that every cell of an imitation has its own survival instinct. He touches a heated wire to blood samples; alien blood recoils, exposing the copies, which are burned. Blair himself proves to be an imitation and has nearly completed a machine that could carry it beyond Antarctica. The survivors destroy Blair and the device, stopping the outbreak before it reaches civilization.

At a remote Antarctic station, the expedition gathers around a block of ice containing a large, unfamiliar body. Members of the party discovered it near a spacecraft buried deep beneath the ice, evidence that both craft and passenger arrived long before recorded human history. Their attempt to uncover the ship destroyed it, but they were able to cut out the frozen creature and bring it back. Blair, the biologist, wants to thaw and examine the specimen. Others are disturbed by its appearance and by the possibility that it is not truly dead. Isolated from the rest of the world by distance and weather, the men must decide whether scientific knowledge justifies releasing an organism that has remained frozen for ages.

The creature is thawed under guard, escapes, and attacks the station's sled dogs. The men interrupt it while it is changing into an imitation of the animals and destroy the mass with fire and electricity. Examination shows that the intruder can absorb another organism and reconstruct itself in that organism's form. The copy can reproduce outward appearance and learned behavior closely enough to pass among familiar companions. Blair calculates that if even one imitation reaches populated country, it could spread until little or no ordinary life remains. Overcome by the implications, he smashes the aircraft, disables the radio, and kills more dogs so that nothing can leave the station. The others subdue him and confine him in a separate building, but his warning remains: the visible creature may not have been the only one.

The expedition tries to determine whether any man was copied while alone. Connant, who guarded the thawing creature, becomes an early suspect, but appearance, memory, and ordinary medical examination cannot establish the truth. A proposed blood-serum test fails when the station's stored blood is destroyed, an act that itself proves at least one imitation is already acting covertly. Trust collapses: the men cannot safely divide into small groups, and even those designing a test may be alien copies protecting themselves. McReady takes control of the investigation and keeps the group together under armed watch. He focuses on the creature's biology, reasoning that a successful test must provoke a response an imitation cannot consciously suppress.

McReady concludes that every separated piece of alien tissue is a complete, self-protecting organism. He heats a wire and applies it to blood drawn from each man. Human blood does nothing; blood from an imitation recoils independently, immediately exposing the copy it came from. With this test the group identifies alien duplicates and burns them before they can change shape or escape. Attention then returns to Blair, still isolated in an outbuilding. The men discover that Blair has been imitated and has dug a concealed space beneath the structure. There the creature has been constructing a compact advanced machine capable of carrying it away from Antarctica. McReady and the surviving humans destroy the Blair imitation and its device with fire. The station is left damaged and its population reduced, but the organism has been stopped just before it could reach the rest of the world.

McReady realizes that an imitation is not merely one animal: every fragment of its tissue is an independent organism concerned with survival. He therefore tests blood samples with a heated wire. Human blood remains inert, while blood belonging to an imitation recoils and exposes its owner. The test allows the surviving men to identify and destroy the copies among them with fire. They then turn to Blair, who had been isolated after wrecking the station's means of transport and communication. Blair has already been replaced and has secretly tunneled beneath his shelter, where he is building an advanced device that would let the creature escape Antarctica. McReady and the others burn the Blair imitation and destroy its work before it can leave. The immediate threat is contained, and the survivors understand that the creature came close to reaching the wider world, where its ability to reproduce through imitation could have replaced terrestrial life.