When the tale begins, a strange and sudden malady is claiming the lives of the local peasants in Styria. Laura, an innocent girl of eighteen, lives a lonely life there with her loving father and two governesses.

Then a dramatic coach crash on Laura's doorstep brings a mysterious, beautiful, but languorous young woman to stay with them. This is Carmilla.

Carmilla becomes deeply attached to Laura, and embarrasses her with her wild outbursts of affection. Laura is deeply drawn to her, but also repulsed. When Laura falls gradually ill, exhausted and melancholic, she is unaccountably loathe to tell anyone. She has vivid dreams—one of a huge black cat prowling her bedroom, another of being kissed and caressed.

Eventually her mother's voice warns her to beware the assassin, revealing Carmilla in a blood-stained nightgown.

Innocently, Laura interprets this as a sign that Carmilla is being murdered.

She rouses the household, but when they break down the door to her room, Carmilla is gone.