Sam, a passionate musician residing in Paris, embarks on a journey when he goes to retrieve some music tapes from his ex-girlfriend, Fanny, who is hosting a lively party. Throughout the chaotic festivity, Fanny repeatedly brushes him off until finally revealing that the tapes are stashed in her office. However, as Sam makes his way there, he is inadvertently knocked into by a guest, leading to an unexpected nosebleed. Just as he starts to regain his composure, he passes out, oblivious to the eerie disturbances happening outside the office door.
Upon waking the next morning, Sam is shocked to find the apartment in disarray, stained with blood and void of any people. Curiosity leads him to the stairway, where he encounters a horrific sight: a zombified Fanny and others who lunge at him as he calls for her. In a desperate bid for safety, he barricades himself inside her apartment. Through a window, he witnesses a family attempting to escape from a neighboring building, only to be devoured by the swarming horde of zombies as they try to flee in their car. In this nightmarish scenario, the apartment becomes Sam's only refuge, providing him a thin veneer of safety against the silent, speedy, and relentless undead that seem to have overtaken Paris.
As the days drag on with no hope of escape, Sam begins to tidy up the mess around him, trying to maintain some semblance of normality. However, his efforts come to a crashing halt when a shotgun blast from the apartment below echoes through the space. Peering through a widened hole in the floor, he discovers the grim aftermath of a suicide committed by one of the residents, who had shot his wife after she had turned into a zombie. Seizing the shotgun, Sam ventures outside but finds the stairway absent of zombies, prompting him to quickly seal himself inside the building once more.
Determined to survive, Sam explores the various units of the building, most of which he finds unoccupied, but he wisely barricades one floor after a nearly fatal encounter with a lurking horde. During his explorations, he discovers a zombified elderly man in the lift, whom he names Alfred as he engages in one-sided conversations with the creature. Stocking up on supplies and rediscovering musical instruments, Sam begins to entertain himself, but the passage of time soon bleeds into a struggle against loneliness and insanity.
In a moment of desperation, he attempts to catch a stray cat that roams among the zombies, nearly meeting his end in the process. During this chaotic endeavor, he accidentally shoots at the cat in a fit of rage, fearing he might have been bitten. As winter closes in, Sam faces even greater challenges with dwindling heat and a non-functional water supply, relying on rainwater and makeshift fireplaces to survive. His mental stability deteriorates further, spurred on by the sight of empty streets and the threat posed by the zombies.
In his increasingly erratic state, Sam decides to test the zombies' awareness by unleashing a thunderous rhythm from his drum set, only to have them return in a chaotic frenzy, nearly infringing upon his apartment with their numbers. That night, a commotion prompts him to fire his shotgun through the door, inadvertently injuring another survivor. In an effort to help, he finds a woman named Sarah, who shares details of her survival tactics with him as they trade stories. However, he is horrified to find that his conversations with her were merely vivid hallucinations, accentuated by the tragic reality that he had previously shot her.
Heartbroken by her loss, he prepares to leave the building, destroying the music tapes that symbolized his past by burning them, inadvertently triggering a fire alarm. The resultant chaos draws a horde of zombies to the building, forcing Sam to navigate through the smoke and danger to reach the roof. There, he makes a daring leap across to another building, where he gazes out at the seeming infinity of the Paris skyline, left with the chilling possibility that other survivors may exist out there, hidden amidst the chaos.
