Scientists and American Air Force officials fend off a blood-thirsty alien organism while at a remote arctic outpost.

Dr Miles Bennell returns his small town practice to find several of his patients suffering the paranoid delusion that their friends or relatives are impostors. He is initially skeptical, especially when the alleged dopplegängers are able to answer detailed questions about their victim's lives, but he is eventually persuaded that something odd has happened and determines to find out what is causing this phenomenon. This film can be seen as a paranoid 1950s warning against those Damn Commies or, conversely, as a metaphor for the tyranny of McCarthyism (or the totalitarian system of Your Choice) and has a pro- and epilogue that was forced upon Siegel by the studio to lighten the tone.

The sensationalist reporter Michelle Fox presents the TV show Weird World, with phony matters about UFOS and aliens. When she hears about Cat, a young woman that claims that have been abducted with her boyfriend and become pregnant by aliens, she convinces her chief to travel with a team to the remote Welsh island of Scalled to interview Cat. She invites the cameraman Ricky Anderson with his sound technician partner; the nerd expert in "ufology" and "ley lines" Gavin Gorman; the actress Candy Vixen and an obscure gay actor to prepare the matter. They get a van and wait for the low tide to reach the island, and when they find evidences that aliens are really landed in the location, the ambitious Michelle decides to film her way to fame and wealth.

Extra-terrestrials flying in high tech flying saucers contact scientist Dr. Russell Marvin as part of a plan to enslave the inhabitants of Planet Earth.