Le Fanu presents the story as part of the casebook of Dr. Hesselius, whose departures from medical orthodoxy rank him as the first occult detective in literature.[6]Laura, the teenage protagonist, narrates, beginning with her childhood in a "picturesque and solitary" castle amid an extensive forest in Styria, where she lives with her father, a wealthy English widower retired from service to the Austrian Empire. When she was six, Laura had a vision of a very beautiful visitor in her bedchamber. She later claims to have been punctured in her breast, although no wound was found.Twelve years later, Laura and her father are admiring the sunset in front of the castle when her father tells her of a letter from his friend, General Spielsdorf. The General was supposed to bring his niece, Bertha Rheinfeldt, to visit the two, but the niece suddenly died under mysterious circumstances. The General ambiguously concludes that he will discuss the circumstances in detail when they meet later.Laura, saddened by the loss of a potential friend, longs for a companion. A carriage accident outside Laura's home unexpectedly brings a girl of Laura's age into the family's care. Her name is Carmilla. Both girls instantly recognize the other from the "dream" they both had when they were young.Carmilla appears injured after her carriage accident, but her mysterious mother informs Laura's father that her journey is urgent and cannot be delayed. She arranges to leave her daughter with Laura and her father until she can return in three months. Before she leaves, she sternly notes that her daughter will not disclose any information whatsoever about her family, past, or herself, and that Carmilla is of sound mind. Laura comments that this information seems needless to say, and her father laughs it off.Carmilla and Laura grow to be very close friends, but occasionally Carmilla's mood abruptly changes. She sometimes makes romantic advances towards Laura. Carmilla refuses to tell anything about herself, despite questioning by Laura. Her secrecy is not the only mysterious thing about Carmilla; she never joins the household in its prayers, she sleeps much of the day, and she seems to sleepwalk outside at night.Meanwhile, young women and girls in the nearby towns have begun dying from an unknown malady. When the funeral procession of one such victim passes by the two girls, Laura joins in the funeral hymn. Carmilla bursts out in rage and scolds Laura, complaining that the hymn hurts her ears.When a shipment of restored heirloom paintings arrives, Laura finds a portrait of her ancestor, Mircalla, Countess Karnstein, dated 1698. The portrait resembles Carmilla exactly, down to the mole on her neck. Carmilla suggests that she might be descended from the Karnsteins even though the family died out centuries before.During Carmilla's stay, Laura has nightmares of a large cat-like beast entering her room. The beast springs onto the bed and Laura feels something like two needles, an inch or two apart, darting deep into her breast. The beast then takes the form of a female figure and disappears through the door without opening it. In another nightmare, Laura hears a voice say, "Your mother warns you to beware of the assassin," and a sudden light reveals Carmilla standing at the foot of her bed, her nightdress drenched in blood. Laura's health declines, and her father has a doctor examine her. He finds a small blue spot, an inch or two below her collar, where the creature in her dream bit her, and speaks privately with her father, only asking that Laura never be unattended.