In the mist-laden terrains of Styria, during the year 1794, a ghastly figure draped in ragged finery emerges from her grave, claiming the life of an unsuspecting gentleman lured away from the welcoming warmth of a nearby tavern. As she retreats back to the depths of eternal slumber, an alarming revelation strikes her: her shroud has vanished, leaving her in a state of exposed vulnerability. This unexpected predicament pushes her into a fierce clash with Baron Hartog, a relentless vampire hunter whose thirst for vengeance drives him to confront those who have wronged him. In a pivotal moment, his blade cuts through the darkness, decapitating her in a moment of profound brutality.
Years pass, and an extravagant celebration unfolds at the lavish estate of General Spielsdorf for his niece Laura's birthday. The festivities take an intriguing turn with the entrance of a mysterious countess and her enigmatic daughter Marcilla. As the evening progresses, the countess confides in General Spielsdorf about a pressing matter regarding a sick relative, placing Marcilla in his custody. Despite Marcilla's unsettling aura, Laura finds herself forming an unusual bond with her new companion. The captivating dark-haired beauty appears drawn to Laura, her gaze igniting flames of a forbidden passion. However, as days go by, Laura is plunged into horrifying nightmares, tormented by visions of a monstrous cat that seems to stalk and devour her. Her health begins to plummet, and soon, two puncture wounds appear on her breasts—evidence of some malevolent force at work.
As Marcilla mysteriously disappears into the night, General Spielsdorf is propelled to track down Baron Hartog, fueled by an unsettling feeling. At the same time, the countess reconnects with her daughter Carmilla, their relationship entangled in a web of secrets and betrayal. United, they devise a cunning plan to secure hospitality from Mr. Morton, a wealthy Englishman residing in Styria, by feigning a carriage mishap near his estate. Once they gain entry, Carmilla deftly manipulates Mr. Morton into providing refuge for her niece, while secretly nurturing a disturbing fascination for his innocent daughter, Emma. Unfortunately, as Emma's health deteriorates, she too starts experiencing nightmares of the same giant cat, and the unsettling puncture marks appear on her breasts.
With General Spielsdorf departing for Vienna on official matters, leaving Emma in the care of her devoted governess, Mademoiselle Perrodot, Carmilla sets her predatory sights on the unsuspecting villagers. Her nocturnal escapades leave a trail of unexplained deaths, each victim drained of their lifeblood. In the face of rising dread, Renton, Mr. Morton's loyal butler, starts digging into local lore concerning vampires and seeks the help of a doctor—one who once treated Laura—to devise a strategy to protect Emma, who is now gravely ill. Armed with garlic flowers and crucifixes, they make valiant attempts to fend off Carmilla, who has morphed into a deadly entity. However, their battle becomes futile when Carmilla savagely murders the doctor, subsequently ensnaring Renton in her web of seduction as he unwittingly dismisses the threat posed by Mademoiselle Perrodot. Fully aware she has been exposed, Carmilla discards Renton and plots to retreat to her tomb, intent on claiming Emma as her lover.
Meanwhile, Mr. Morton rushes back to his estate after receiving an urgent message from Renton. To his shock, he finds General Spielsdorf and Baron Hartog at the ruins of Karnstein Castle, accompanied by Laura’s fiancé Carl. Hartog unveils a dark history regarding the Karnstein family—a notorious clan of vampires he almost annihilated in his youth, including the very female vampire responsible for the death of his sister. Still, he could not discover the final resting place of Mircalla Karnstein. As Spielsdorf and Morton gaze upon her haunting portrait within the castle, the dreadful realization dawns that Marcilla and Carmilla are, in fact, the same entity they’ve encountered.
Driven by a sense of urgency, Carl rushes back to Mr. Morton's estate, determined to rescue Emma from Carmilla’s clutches. In the midst of an escalating battle, Mademoiselle Perrodot pleads to accompany Mircalla, only to meet a gruesome fate at the hands of the vampire. Just as Carl arrives, he wields a poignard with a cross, effectively repelling Mircalla, who dissipates into the night and retreats back towards Karnstein Castle, where Spielsdorf, Hartog, and the others patiently wait for her return.
Upon discovering her burial site, General Spielsdorf exacts a brutal revenge by plunging a stake through Carmilla's heart and decapitating her, finally avenging his daughter's untimely demise. Emma is liberated from the vampire’s dark grasp, and as the curse lifts, Mircalla’s portrait on the wall grotesquely transforms into a skeletal visage adorned with fangs. Observing this dark saga unfold from the shadows is a baleful man cloaked in black, examining the chaos with a look of contemptuous amusement.
