In Anchorage, journalist Ned Scott (Douglas Spencer), looking for a story, visits the Air Force officer's club, where he meets Captain Pat Hendry (Kenneth Tobey), his co-pilot Lieutenant Eddie Dykes, (a friend of Scott's), and flight navigator Ken "Mac" MacPherson. General Fogarty orders Hendry to fly to Polar Expedition Six at the North Pole, per a request from its lead scientist, Nobel laureate Dr. Arthur Carrington (Robert Cornthwaite); Carrington has radioed that an unusual aircraft has crashed nearby. With Scott, Corporal Barnes, crew chief Bob, a pack of sled dogs, Hendry pilots a Douglas C-47 transport to the remote outpost.
Upon arrival, Scott and the airmen meet radio operator Tex, Mrs. Chapman, Lee, one of two cooks, and the Inuit dog handlers. Also present are scientists Vorhees, Stern, Redding, Stone, Laurence, Wilson, Ambrose, Auerbach, Olson, Mrs. Chapman's husband Dr. Chapman, and Carrington. Hendry later rekindles his romance with Nikki Nicholson (Margaret Sheridan), Carrington's secretary. Several scientists fly with the airmen to the crash site, finding a large object buried beneath melted ice. As they spread out to determine its shape, they realize they are standing in a circle; they have discovered a flying saucer. The team attempts to melt the ice covering the saucer with thermite, but a violent reaction with the craft's metal alloy completely destroys it. Their Geiger counter, however, detects something, a frozen body, buried nearby; it is excavated in a large block of ice and loaded aboard the transport. They fly out as an Arctic storm closes in on the site.
Hendry assumes command of the outpost and denies Scott permission to send out his story; he also denies the scientists' demands to examine the body. Tex sends an update to Fogarty, and the airmen settle in as the storm arrives. A watch is posted; Barnes relieves McPherson and, disturbed by the creature's appearance in the clearing ice, covers it with an electric blanket, which he does not realize is plugged in. The block slowly thaws and the creature, still alive, escapes into the storm and is attacked by the sled dogs. The airmen recover the creature's severed arm after the attack.
The scientists examine the arm, concluding that the alien is an advanced form of plant life. Carrington is convinced of its superiority to humans and becomes intent on communicating with it. The airmen begin a search, which leads to the outpost's greenhouse. Carrington stays behind with Vorhees, Stern, and Laurence, having noticed evidence of alien activity. They discover a third sled dog hidden away, which has had all of its blood drained; the creature feeds on blood. Carrington and the scientists post a secret watch of their own, hoping to encounter the alien before the airmen find it.
The next morning, the airmen continue their search. Tex informs them that Fogarty is aware of their discovery and demands further information, now prevented by the fierce storm. Stern appears, badly injured, and tells the group that the creature has killed Auerbach and Olson. When the airmen investigate, the alien attacks them; they manage to barricade it inside the greenhouse. Hendry confronts Carrington and orders him to remain in his lab and quarters.
Carrington, obsessed with the alien, shows Nicholson and the other scientists his experiment: Using seeds taken from the severed arm, he has been growing small alien plants by feeding them from their blood plasma supply. Hendry finds the plasma missing when it is needed to treat Stern, which ultimately leads him back to Carrington. Fogarty transmits orders to keep the creature alive, but it escapes from the greenhouse and attacks the airmen in their quarters. They douse it with buckets of kerosene and set it afire, forcing it to retreat into the storm. After regrouping, they realize that their building's temperature is falling rapidly; the furnaces have stopped working, sabotaged by the alien. They retreat to the station's generator room to keep warm, and rig an electrical "fly trap". The alien continues to stalk them, but at the last moment, Carrington attempts to communicate, pleading with the creature. It knocks him aside, walks into the set trap, and is electrocuted and reduced to just a pile of ash on Hendry's direct order.
When the weather clears, Scotty is finally able to file his "story of a lifetime" by radio to a roomful of reporters in Anchorage. He begins his broadcast with a warning: "Tell the world. Tell this to everybody, wherever they are. Watch the skies everywhere. Keep looking. Keep watching the skies".