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.

In Downey, the teenagers Chris, Scott and Tim are best friends and decide to drive to a bar downtown to a grungy band's gig. Chris' girlfriend Jackie, meanwhile, goes to a party with her preppy friends. While heading downtown, the trio of friends note that there are no cars on the roads despite the rush hour and then they find that the streets are empty. When they arrive in their destiny, they are chased by zombies and run to the bar. Chris decides to return to Downey while Jackie and her friends are attacked by a bunch of zombies.

Kathleen, a bride to be, and her four bridesmaids Sophia, Jessica, Beth, and Amber travel to Mexico in hopes of having a last "hoorah" before the wedding a few weeks away. After partying hard the night before, Sophia splits from the group to pursue Rob, a hansom young tourist from the states. The other girls decide to take a tour of the countryside without her, but are robbed and left for dead in a remote rugged terrain. As night falls, the tired and injured girls arrive at an abandon resort and decide to take shelter until morning. When they enter, strange things begin to happen, as the girls become overwhelmed by an unspoken evil that possesses the resort. Back in town, Sophia is worried about her friends and works hard to track them down. After realizing they took a scenic tour, Sophia and Rob do the same, in hopes of finding her lost friends. Sophia and Rob finally discover the resort and attempt to help their friends...