Who Goes There?
John W. Campbell
 A group of scientific researchers, isolated in Antarctica by the nearly-ended winter, discover an alien spaceship buried in the ice, where it crashed twenty million years before. They try to thaw the inside of the spacecraft with a thermite charge, but end up accidentally destroying it when the ship's magnesium hull is ignited by the charge. However, they do recover the alien pilot from the ancient ice, which the researchers believe was searching for heat when it was frozen. Thawing revives the alien, a being which can assume the shape, memories, and personality of any living thing it devours, while maintaining its original body mass for further reproduction. Unknown to them, the alien immediately kills and then imitates the crew's physicist, a man named Connant; with some 90 pounds of its matter left over it tries to become a sled dog. The crew discovers the dog-Thing and kills it in the process of transformation. Pathologist Blair, who had lobbied for thawing the Thing, goes insane with paranoia and guilt, vowing to kill everyone at the base in order to save mankind; he is isolated within a locked cabin at their outpost. Connant is also isolated as a precaution and a "rule-of-four" is initiated in which all personnel must remain under the close scrutiny of three others. The crew realizes they must isolate themselves and therefore disable their airplanes and vehicles, while pretending things are normal over their radio transmissions to prevent any rescue attempt from civilization. The researchers try to figure out who may have been replaced by the alien (simply referred to as the Thing), in order to destroy the imitations before they can escape and take over the world. The task is almost impossibly difficult when they realize that the Thing is also telepathic, able to read minds and project thoughts. A sled dog is conditioned by human blood injections to provide a human-immunity serum test, as in rabbits. The initial test of Connant is inconclusive as they realize that the test animal received both human and alien blood, meaning that either Doctor Copper or expedition Commander Garry is actually an alien. Assistant commander McReady takes over and deduces that all the other animals at the station, save the test dog, have already become imitations; all are killed by electrocution and their corpses burned. Everyone suspects each other by now but must stay together for safety, deciding who will take turns sleeping and speculating when the patient monsters will finally have the upper hand. Tensions mount and some men begin to go mad thinking they are already the last human or wondering if they would even know if they weren't human any longer. Ultimately, one of the crew members is murdered and accidentally revealed to be a Thing. McReady realizes that even small pieces of the creature will behave as independent, selfish organisms. He then uses this weakness to test which men have been "converted" by taking blood samples from everyone and dipping a heated wire in the vial of blood. Each man's blood is tested, one at a time, and the donor is immediately killed if his blood recoils from the wire; fourteen in all, including Connant and Garry, are revealed as aliens. They go to test the isolated Blair and on the way see the first albatross of the Antarctic Spring flying overhead; they shoot the bird to prevent a Thing from taking it over and flying to civilization. When they reach Blair's cabin they discover he is a Thing. They realize that it has been left to its own devices for a week, coming and going as it pleased, able to transform itself by squeezing under doors. With the creatures inside the base destroyed, McReady and two others enter the cabin to kill the Thing that was once Blair. McReady systematically forces it out into the snow and methodically destroys it with a blowtorch. Afterwards the trio discover that the Thing was dangerously close to finishing construction of an atomic-powered anti-gravity device that would have allowed it to escape to the outside world. "No, by the grace of God, who evidently does hear very well, even down here, and the margin of half an hour, we keep our world, and the planets of the system too. Anti-gravity, you know, and atomic power. Because They came from another sun, a star beyond the stars. They came from a world with a bluer sun."