At the remote Alpine village of Trollenberg, someone or something is killing off mountain climbers. The culprits turn out to be an army of one-eyed, tentacled beasts from outer space, who hide themselves in a radioactive cloud. Crawling along like snails, these horrific creatures attempt to neutralize their human foes by pumping a freezing fog at their pursuers. It matters not at all that some of the locals have been mentally enslaved by the monsters. It's up to American scientist Alan Brooks to save the day.
Stephen King considered it one of the scariest of the many horror movies he saw as a kid, and the climax of It features the eye monsters. It was also a big part of the inspiration for John Carpenter's The Fog.
Tropes used in the film:
- Adult Fear: The woman who notices her little daughter is missing during the evacuation.
- Benevolent Conspiracy: Alan and Prof. Crevett are part of a low-level one, having limited experience with the monsters already in the backstory, though they're never come face-to-eyeball with the things.
- Big Sister Instinct: Anne's sister wants nothing more than to get her the heck out of there.
- Brainwashed and Crazy: A couple of the mountaineers are hypnotized to try to kill Anne.
- Convection Schmonvection: The aliens attacking the observatory are defeated by having an airplane firebomb the observatory. But despite the fact that the aliens had already broken through the walls of the observatory in an attempt to get to Anne, the fires do not spread into the observatory itself and harm any of the people taking shelter there.
- Fainting: Anne does this a lot. Presumably it's due to outside influence.
- Gorn: This film is shockingly gore-soaked for the period in which it was made.
- Hostile Terraforming: The film is about aliens' native air slowly enveloping a mountain and later the surrounding area.
- Molotov Cocktail: Used to fight the monsters.
- Night of the Living Mooks: The aliens are able to reanimate their victims as their own operatives.
- No Hugging, No Kissing: Probably due to the sizable age gap, there is no particular romantic tension between Brooks and either of the Pilgrim sisters.
- Obscured Special Effects: For most of the movie, the aliens stay hidden in the strange cloud on the side of the mountain, although we do eventually get a good look at them.
- Off with His Head!: The aliens' preferred method of murder, apparently for no other reason than the shock value.
- The Professor: Professor Crevett, who runs the observatory.
- Psychic Powers: Anne has some level of mind-reading which she uses for parlour tricks. But she also seems to have a form of clairvoyance which draws her to Trollenberg and which lets her see what the aliens are up to (although she can't detect the aliens themselves).
- Spotting the Thread: The first victim is described as having been decapitated by his belaying rope when it tangled around his neck. It's quickly pointed out that the rope was secured about his waist and could not have gotten around his neck in the first place.
- Starfish Aliens: Big veiny blobs with eyeballs and Combat Tentacles.
- The Stoic: Averted; everyone, including the men, react with realistic horror upon seeing the mutilated victims.
- Whole Plot Reference: Freakazoid! used this as the basis of an entire episode ("The Cloud").