An isolated castle hidden in the darkness of the forests of Austria finds a young woman named Laura living alone with her widower father. Laura relates a strange and bizarre dream from her childhood about a beautiful woman who furtively entered her room and bit her on the chest. Laura grows into a restless teenager desperate for a close friend and her hopes are raised when her father informs her that he has sent for a companion named Bertha. Those hopes are tragically dashed when news arrives that Bertha has suddenly perished. A carriage accident near the castle is about to prove that when a door slams shut, sometimes a window is throw open by a rush of cold, brittle air.
The carriage accident produces an injured victim named Carmilla whom Laura instantly recognizes as the girl who bit her in her childhood dream. Carmilla, it turns out, shared the same dream as a child. Carmilla’s mother was also in the carriage, but announces to Laura’s father that she must continue along on her journey of life and death.
And so Carmilla will be left to stay with Laura at the title.
The two grow very close over the subsequent weeks, although Carmilla remains peculiarly committed to disclosing as little information about her family and past as possible. That’s not the only oddness about the young woman: even for a young woman, she is pretty dang moody, she sleeps during the day and sleepwalks during the night and, quite peculiarly indeed, her anathema toward the sound of Christian hymns far exceeds even the expectations on might have of an attractive young moody sleepwalker recently injured in a carriage accident.
Still, all of that bizarre behavior might be more easily overlooked were it not for the singularly strange demonstration of the unusual which afflict Carmilla: her sexual and romantic attraction to Laura. For her part, Laura finds such attention embarrassing and even repulsive, yet finds herself overpowered by the attention to the point of being incapacitated at the level of rejecting Carmilla. Her new best friend tells Laura that she is hers and shall forever be hers.
This results in a severe anxiety on the part of Laura which manifests itself in the form of nightmares taking the form of being attacked by a small yet ferocious animal that attacks her in the night by biting her chest and transforming her from barely pubescent teen into spectacularly pubescent young woman. Only after the nightmare come to Laura does the full truth about what exactly happened to the unfortunate Bertha become clear.
Bertha, it turns out, was viciously attacked by a young woman not terribly unlike Carmilla with the notable exception that this girl’s name was Millarca. In fact, Millarca arrived at Bertha’s home under eerily similar circumstances to those which brought her inside the is0lated castle occupied by Laura and her father. Upon the realization that Millarca was, in fact, a vampire, the guardian of the estate set a trap her and waited as the vampire arrived not in the form of the beautiful Millarca, but in the guise of a creature that more resembled a freaky cat. The cat creature bit Bertha on her neck before disappearing in human form. Not long after, Bertha expired.
Millarca turns out to be an anagram of Carmilla and the relationship between the two strange women turns out to extend beyond that coincidence. Indeed, Carmilla is the very same vampire as Millarca and both are merely slightly varied incarnations of Countess Karnstein who reportedly died many years before.
Vowing to track down Carmilla and destroy her forever, Laura’s father comes face to face with Carmilla in an exciting showdown within a crumbling church. The novel’s own precursor to Van Helsing—noted vampire specialist Baron Vordenburg—arrives to help by exhumation of the body of the Countess from her place of entombment. The slayer pulls out a wooden stake and drives it into the heart, thus ending Carmilla’s lusty reign of lesbian terror and freeing Laura from her nightmares and the kiss of the vampire forever.