'The Parasite', a novelette by Sir Arthur Conan Doyle, tells the story of Austin Gilroy, a young man studying physiology who becomes involved in the occult. Gilroy is introduced to Miss Penclosa, a middle-aged woman with psychic powers who puts his skeptical fiancée into a trance to prove her abilities. Miss Penclosa becomes infatuated with Gilroy and uses her powers to manipulate him into returning her affection. As the cruel tricks escalate, Gilroy discovers the true extent of her power and the shocking conclusion leaves him reeling.