Without Warning

The father and his son are killed by flying jellyfish-like creatures that pierce their skin with needle-tipped tentacles. The attack occurs in the mountains just as they are about to begin their hunt.

Four teenagers, Tom, Greg, Beth, and Sandy, hike in the same area and ignore warnings from local truck stop owner Joe Taylor. They press on toward the lake where they plan to set up camp.

A group of Cub Scouts and their leader enter the area and are attacked by the alien. The leader is killed, and the scouts flee after an unidentified humanoid crosses their path.

The four teens set up camp at a lake, but after a few hours Tom and Beth vanish without a trace. Sandy and Greg decide to search for them, uneasy about the disappearing friends.

Sandy and Greg discover the bodies of Tom, Beth, the father and son, and the Cub Scout leader inside an abandoned shack. The discovery deepens the sense that something deadly is stalking the area.

The surviving teens drive away in their van, and a jellyfish-like creature attacks the windshield. They shake it off and head toward the local truck stop for safety.

Greg tries to persuade locals to help but most people do not believe him. The bar owner and Sarge are more receptive, making them the few who entertain the possibility of an alien threat.

Waiting in the van outside, Sandy encounters the humanoid and flees into the woods. Meanwhile the bar owner and Sarge decide to keep Greg from going into the darkness to search for her.

Joe Taylor goes to fetch Sandy and brings her to the bar. He reveals that he has faced the creature before and even keeps jellyfish trophies from his encounters.

Lights go out, and the sheriff arrives as paranoia rises. Sarge shoots at what he believes is an invader, only to realize too late that he has harmed a human; the incident triggers his breakdown and he blames Greg.

The group discusses how to prove the creatures exist, while Taylor recounts his past encounter and his jellyfish trophies. They plan to wait for an opportunity to ambush the hunter.

Taylor goes to search the shack and finds the bodies of the earlier victims, confirming the scale of the hunt. He is then attacked by another jellyfish-like creature.

The teens attempt to hide and plan, but Sarge arrives, seizes them, and takes them as if they are aliens. Greg uses a deception to distract him, and they manage to escape by leaping from a bridge.

They reach a house where they can rest and clothes can be changed. Later, Sandy discovers that Greg has been killed by the alien, and Taylor arrives to explain the creature's nature to her.

An ambush plan at the shack leads to a confrontation where Sarge is killed by the alien. Taylor fires with little effect, and Sandy lures the creature into the shack before blowing it up, surviving the horrible night.