Élizabeth Marie-Georges Pascal is traveling by train to Roublès to live with Michel Herval, the owner of the Roublès winemaking vineyard, and she strikes up a friendship with a fellow passenger named Brigitte Brigitte Lahaie on the long journey. The atmosphere on the train grows tense when Brigitte excuses herself to use the restroom and never returns right away. A vineyard worker then boards the carriage, encounters Brigitte, and soon afterwards confronts Élizabeth in her compartment. Before long, the man’s neck bursts into a painful ulcer that begins oozing blood, and Élizabeth flees in a panic, stumbling over Brigitte’s corpse on her way out of the train.
She bolts from the train and seeks help in a nearby village. There she is taken in by Pierre Patrice Valota and his daughter Antoinette Patricia Cartier, who respond with a cold reserve to Élizabeth’s alarming tale. As her fear grows, Élizabeth notices Pierre’s arms are badly infected and disfigured; Antoinette attempts to reassure her, guiding Élizabeth upstairs to rest. In the bedroom Élisabeth discovers a dead woman with a throat cut—Antoinette explains that the woman is her mother and that Pierre killed her because his mind has begun to unravel. Élizabeth and Antoinette try to leave, but Pierre, now bearing the same grotesque ulcers, bursts into the room and rips open Antoinette’s blouse to reveal his infected body. He murders Antoinette with a pitchfork, and Élizabeth escapes, grabbing Pierre’s car and driving away as he collapses in front of it, pleading for her to run him down—an order she reluctantly follows.
Her flight continues as more bodies afflicted with the same ulcers appear in the village, and the infected stumble about like zombies, driven to murderous frenzy by the illness. A man with ulcer-covered head begs Élizabeth for help, and when the pain drives him to smash the car’s window, she shoots him with a revolver from the glove compartment. She then encounters Lucie [Mirella Rancelot], a blind girl searching for her caregiver, Lucas. While Élizabeth assists Lucie, the village is revealed to be strewn with corpses and overwhelmed by the spread of infection, with some townsfolk acting like mindless predators. Lucie later heads off to find Lucas and is tragically killed and decapitated by Lucas, who has himself become infected.
A blonde woman—still alive and seemingly uninfected—rescues Élizabeth and helps her escape a group of pursuing infected. This woman has been trapped in a house for days, and when she briefly reveals herself to the others by disrobing, Paul Félix Marten and Lucien Serge Marquand are convinced she is safe and tell her to wait by their truck. Élizabeth and the woman manage to reach the truck but a clash ensues; Élizabeth clubs the woman with a torch, exposing the woman’s own infection boils. The woman then hurls the torch into a dynamite crate in the truck, causing a devastating explosion that kills her and destroys the vehicle.
Elizabeth, Paul, and Lucien continue their trek on foot toward the vineyard, where they hope to find answers. They learn the authorities are already aware of the outbreak. Inside the abandoned estate, Élizabeth discovers Michel [Michel Herval] infected but lucid. He explains that he invented the pesticide that tainted the wine, which has contaminated the population at a terrifying pace. His illegal use of immigrant labor prevents him from alerting the police sooner, a choice he now regrets.
Michel urges Élizabeth to stay away, but she embraces him; Paul returns searching for Élizabeth and finds the two together. In a moment of panic and despair, Michel makes a final, violent move toward Paul, forcing Paul to shoot him. Now newly infected, Élizabeth seizes Paul’s gun and shoots him, then ambushes and kills Lucien when he confronts them. The film closes on Élizabeth, who silently allows Michel’s blood to drip onto her face from the loft above, leaving the outcome of her fate shrouded in ambiguity as the outbreak continues to unfold.
