Late one evening, Allan Gray, Nicolas de Gunzburg, a wandering student of the occult, arrives at an inn near the village of Courtempierre, France, and rents a room. He is awakened by an old man who enters the locked room and leaves a small rectangular package on the table with "To be opened upon my death" written on the wrapping paper. Feeling drawn to investigate, Gray takes the package and leaves the inn.
Gray follows the shadow of a peg-legged soldier to a disused factory, where the shadow reunites with its body, and other shadows dance. He also encounters an old woman who seems to hold sway over the shadows, and an old man with a mustache who shows Gray the door. The old woman from the factory, Henriette Gérard, lingers in the memory as a haunting thread.
Following more shadows to a manor house, Gray looks through a window and sees the lord of the manor, the man who gave him the package, Maurice Schutz shot by the shadow of the soldier. Gray gets the attention of an old servant, Albert Bras, and they rush to the manor, but it is too late to save him. Giséle, the lord of the manor's younger daughter, is there when he dies, but her sister, Léone, does not leave her bed, gravely ill. A coachman is sent to get the police, and the old servant's wife, N. Babanini, invites Gray to stay the night.
In the library, Gray opens the package and finds a book about horrific demons called vampires. As he begins to read about how the creatures suck blood and gain control over the living and dead, Giséle says she sees Léone walking outside. They follow her, and, when they catch up, see the old woman from the factory bent over Léone's unconscious body. The old woman slinks away, and Léone, who is discovered to have fresh bite wounds, is carried back to bed. The carriage returns, but the coachman is dead.
The village doctor visits Léone at the manor, and Gray recognizes him as the old man with a mustache that he saw in the factory. The doctor tells Gray that Léone needs a blood transfusion, and Gray donates blood. Exhausted from blood loss, Gray falls asleep.
Meanwhile, the old servant has noticed the book and begun to read it. He learns that a vampire can be defeated by opening its grave at dawn and driving an iron bar through its heart, and that there are rumors that a vampire was really behind a previous epidemic in Courtempierre, with a woman named Marguerite Chopin being the prime suspect.
Gray wakes up sensing danger and rushes to Léone's bedside, where he stops her from drinking poison that the old woman had the doctor bring to the manor. The doctor flees, kidnapping Giséle, and Gray follows. Just outside the factory, Gray trips and has an out-of-body experience, in which he sees himself dead, sealed in a coffin with a window, and carried away to be buried. After his spirit returns to his body, he notices the old servant heading to Marguerite Chopin's grave. They open the grave and find the old woman perfectly preserved, until they hammer a large metal bar through her heart, at which point she becomes a skeleton. The curse of the vampire is lifted, and, back at the manor, Léone suddenly recovers.
The ghost of the lord of the manor appears to the doctor, causing him to run away and the soldier to fall to his death down a flight of stairs. Using information he gathered during his out-of-body experience, Gray finds and unties Giséle. The doctor tries to hide in an old mill, but the old servant, seemingly aided by an unseen force, locks the doctor in a chamber where flour sacks are filled and activates the mill's machinery, which fills the chamber with flour and suffocates the doctor. Giséle and Gray cross a foggy river in a boat and find themselves in a bright clearing.
