The Earth passes through the tail of a comet for the first time in 65 million years. Eleven days before Christmas, crowds gather to watch the skies. 18-year-old Regina Belmont (Catherine Mary Stewart) works in a movie theatre in Southern California, and today she is angry because somebody else, with the handle of DMK, has won a video game, breaking her perfect record. She stays after work to help her boyfriend Larry (Michael Bowen) abscond with a movie to make an illegal copy. They stay to have sex in the steel-lined projection booth. Reggie’s 16-year-old sister Samantha (Kelli Maroney) argues with their stepmother Doris (Sharon Farrell). She thinks her mother is cheating on their father, who is away with the military. After the argument, she goes and spends the night in a steel backyard shed.
The next morning, the sky is colored with a reddish haze and there are no people—only piles of red dust and clothing. Larry is killed by a zombie with a pipe wrench. After playing a video game, Reggie goes looking for Larry and has to flee the zombie on Larry’s motorcycle. She and her sister Sam believe they have been saved by being surrounded steel as the comet passed by.
They hear a disc jockey on the air and go to the station to check it out, but the show was pre-recorded. They run into Hector Gomez (Robert Beltran), who spent the night in the back of his steel truck. Sam speaks on the microphone and is heard by researchers in a steel underground bunker in the desert. The scientists think the zombies will eventually be piles of dust themselves. Hector leaves to check on his family.
Reggie and Sam go shopping for guns and clothing at the mall. After a firefight with the evil stock boys, the girls are taken prisoner, but saved by the scientists’ rescue team. Reggie has a rash, so one of the scientists, Audrey White (Mary Woronov) thinks she has been exposed to the virus. She pretends to euthanize her, but only injects a sedative and kills the other scientists. Audrey White is the one who has been exposed, and she euthanizes herself. Sam and Hector set out to rescue Reggie.
The scientists, it seems, had left the ventilator open on their steel building during the comet’s passage. Reggie, having escaped, discovers the scientists are using the blood of survivors to keep themselves alive. Reggie saves some kids and unplugs some unfortunates. Sam and Hector arrive and blow up the scientists. After the rain washes away the dust, Reggie pairs up with Hector and they assume parental roles. Sam drives off with another survivor, named Danny Mason Keener (Marc Poppel), whose license plate is DMK.
The film was written and directed by Thom Eberhardt. The lighthearted and adventuresome film was only produced because of the popularity of the Valley Girl song by Moon Unit Zappa and films like Repo Man. Joss Whedon says it influenced his creation of Buffy the Vampire Slayer. The cops in Samantha’s nightmare were real cops who stopped traffic for the film. Shots of the empty street were done early in the morning or when the lights were red. Kelli Maroney played the head cheerleader in Fast Times at Ridgemont High. Robert Beltran was Chakotay on Star Trek Voyager. Catherine Mary Stewart was in The Last Starfighter.