Jack, Bruce Campbell is a convicted murderer being transported in a police wagon through a raging blizzard when the vehicle crashes into a tree. The officers and the prisoner press on through the storm, eventually seeking shelter at a small airport. In the tense, confined space of the airport, the story tightens as danger closes in.
In a restroom, an alien disguised as a preacher ambushes the officers and reveals a plan to invade and take over Earth. Jack fights back and kills the alien, who disintegrates into nothingness, leaving the others shaken and unsure of who to trust.
The pilot and the passengers waiting for their flight mistakenly believe Jack the prisoner is behind the killings. A second woman is killed in a scuffle and her body also disintegrates, confirming the eerie truth. The group ropes Jack to a post and begs the pilot to fly, but the brutal blizzard makes any departure risky. A ruthless businessman threatens the pilot with a gun and shoots a human serviceman who blocks his path, killing him. Jack seizes the moment, wresting the weapon back and turning the tables.
The baggage x-ray reveals that an elderly woman is an alien, and she kills the airport security guard. With radio communications failing, the pilot heads for the hangar and improvises a means to reach out using a radio found by children there. The children, who belong to no one, reveal themselves as aliens while Jack escapes with the pilot. They discover a small, two-person biplane and decide to flee to Canada to avoid capture and prosecution.
The remaining passengers barricade themselves in the lounge, determined to withstand the alien threat. They discover boxes containing a tool for clearing avalanches and use it to fight back when the aliens strike through the back of a vending machine, though two more passengers are killed in the confrontations.
The pilot and Jack crawl back through the air ducts to the main hall, rescuing the surviving passengers along the way as the aliens close in on the lounge. They all eventually make it back to the hangar, though the ruthless businessman falls victim to the invaders.
On the surveillance feed, they realize that Darian, Kedar Brown, a leading alien, is still alive in the lounge. The pilot and Jack slip back to save him, narrowly avoiding a pursuing alien and setting the attacker ablaze with gasoline as they race toward safety.
Just as the pilot is about to fly Jack away, Darian tries to bluff his way to victory by disguising his voice as the pilot and accusing Jack of the murders. He uses mind-controlling handcuffs on a passenger to coerce a confession, but the pilot refuses to blame Jack. Jack also reveals that he removed the bullets from the gun, a small but crucial detail that shifts the balance. United by their resolve, the surviving humans overpower the alien and throw it into a moving propeller, ending the immediate threat. With police sirens drawing near, the pilot honors her vow and flies Jack to Canada, a tenuous escape from justice and a fragile glimmer of hope for survival.
