A father and son go hunting in the mountains. Before they can begin hunting, which the son does not want to do anyway, they are killed by flying jellyfish-like creatures, which penetrate their skin with needle-tipped tentacles. Some time later, four teenagers, Tom, Greg, Beth and Sandy, hike in the same area, ignoring the warnings of local truck stop owner Joe Taylor. A group of Cub Scouts is also in the area; their leader is also killed by the alien creatures, while his troop runs into an unidentified humanoid and flee. The teenagers set up camp at a lake, but after a few hours, Tom and Beth disappear. Sandy and Greg go looking for them and discover their bodies in an abandoned shack. They drive away in their van, while being attacked by one of the jellyfish which tries to get through the car's windshield. After they get rid of it, they arrive at the truck stop. Greg tries to get help from the locals, but they do not believe him, except for Fred 'Sarge' Dobbs, who is a mentally illveteran. Meanwhile, Sandy encounters the humanoid and flees into the woods, where Joe Taylor finds and returns her to Greg. While they discuss the situation, the sheriff arrives, but Sarge shoots him and begins to become more paranoid. Greg and Sandy leave with Taylor, who reveals he has been attacked by the humanoid before and secretly keeps the flying jellyfish as trophies. They search for the shack and once there, Taylor goes inside to only find the bodies of Tom, Beth and the cub scout leader. They discuss waiting for the creature when Taylor is attacked by another "jellyfish". The young people run once again, leaving him behind as ordered. They stop a police car and get into the back seat, but find Sarge driving. He abducts them, believing them to be aliens. Greg plays along, telling the deranged man that an invasion force is on the way, thus distracting him enough to toss him aside, run away with Sandy and jump from a bridge. They make it to a house where they find new clothing and try to relax. In the night, Sandy wakes up and goes looking for Greg, only to discover that he has been killed by the alien, who is still in the room. She flees to the basement and the creature is about to get her when Taylor arrives and saves her. On the way to the shack, he tells her about the creature: it is a tall extraterrestrial who hunts humans for sport to keep as trophies, using the living creatures as living weapons against its prey. They wait at the shack to ambush the hunter with dynamite when Sarge shows up, almost spoiling their plan. He and Taylor fight, and Sandy is about to hit Sarge from behind when the alien arrives and kills Sarge. Taylor then shoots the creature, with little to no effect. Realizing the last chance of success, he lures it to the shack, which is then blown up by Sandy. She alone survives the horrible night.
Dread Central gave the home release of Without Warning 3 1/2 out of 5 blades, singling out the Blu-ray's special features out as a highlight and giving them 4 out of 5 blades. DVD Talk recommended the movie, writing "Without Warning may not be a lost masterpiece but it is a really entertaining low budget horror picture that makes the most of its effects set pieces and a few notable cast members." The A.V. Club praised the performances of veteran actors Martin Landau and Jack Palance and called some of the special effects "damn gross".
