A comet, which hasn't graced Earth's vicinity in 65 million years, is set to make its return, creating a mix of excitement and concern among people. While most celebrate with parties, a select group of scientists takes refuge in a bunker located in the desert near Los Angeles, fearful of the potential effects of the comet's tail.
On that same fateful night, 18-year-old Regina Belmont (Catherine Mary Stewart) is busy working as a theater usher. Instead of heading home post-show, she informs her stepmother, Doris (Sharon Farrell), that she'll be out with her science class at the observatory. Instead, she plans to spend the night with her semi-boyfriend, Larry (Michael Bowen), and engage in intimate activities in the steel-lined projection room. Larry, meanwhile, is waiting for the return of a film he lent out so they can create a pirated copy.
At their home, Regina's vivacious 16-year-old cheerleader sister, Samantha (Kelli Maroney), finds herself in a heated argument with Doris, accusing her of infidelity while their father is serving in the military in Honduras. Following a tense exchange, Doris strikes Samantha, prompting her to leave the house in anger.
The next morning, Regina and Larry awaken only to find that the film has not been returned. Larry steps out to retrieve it, leaving Regina to her own devices. As she fills the time playing an arcade game, she astonishingly beats a high score left by someone with the initials "DMK." Unfortunately, while Larry ventures out, he meets a gruesome end when he is violently assaulted and killed by a zombie.
Regina, sensing something is amiss upon discovering Larry's motorcycle still parked, heads outside to investigate. She soon encounters the zombie herself but, thanks to her father's self-defense training, manages to flee on the motorcycle. Racing home, she finds a chilling scene—empty streets, abandoned clothes, and a scarlet-tinged sky. It dawns on her that a catastrophe has occurred, and to her relief, she discovers Samantha is still alive, albeit unaware of the global devastation.
Samantha recounts her night spent hiding in the garden shed after running away, blissfully unaware that the world outside has turned to chaos. Regina theorizes that the protection offered by the steel projection room and shed might have shielded them from the comet's deadly effects. They tune in to the radio, where they discover that the local station is still operational. This leads them into the city in search of survivors.
Upon arriving at the radio station, Regina and Samantha encounter Hector Gomez (Robert Beltran), who has a revolver pointed at them, ensuring they are not zombies. Hector recounts his harrowing tale of survival, which includes a teenage girl who didn’t make it. He joins the sisters in their quest for answers.
As Samantha broadcasts a desperate message for any living soul to contact them, they receive a call from a group of scientists in an underground bunker. They learn that the comet's effects have turned most of humanity to dust, with those partially exposed facing a grim, undead fate. The scientists assure them that assistance is on the way, but Hector feels compelled to check on his family in San Diego.
Back at the bunker, tensions rise between scientists as they deliberate whether to include outsiders in their survival plan. Meanwhile, Samantha and Regina arm themselves from a local military stockpile, leveraging their father's firearms training. When they unwittingly attract unwanted attention from a group of former stock boys, what begins as a shopping spree quickly escalates into chaos.
The capture of the sisters leads to a deadly game of Russian Roulette, interrupted by the timely arrival of the scientists who rescue them. However, misunderstandings regarding Samantha’s exposed status lead to further entanglements. In a twist of fate, Regina discovers that the bunker harbors dark secrets about the fate of other survivors.
As the tension mounts, sibling bonds strengthen, leading to a high-stakes escape. Ultimately, the girls navigate the cleared remnants of Los Angeles, forming a makeshift family with Hector and two young survivors. Regina captures precious moments of their newfound lives amid the chaos.
The story concludes with a newfound hope for Samantha as she crosses paths with a handsome teenager named Danny Mason Keener ([Marc Poppel]), suggesting that life continues in unexpected ways, even in the aftermath of disaster. As they set off in his car, his license plate reading "DMK" hints at the normalcy once lost but now slowly returning.
