The Parasite is a 1894 novelette by Sir Arthur Conan Doyle.

The main character is a young man known as Austin Gilroy. He studies physiology and knows a professor who is studying the occult. The young man is introduced to a middle-aged woman known as Miss Penclosa, who has a crippled leg and psychic powers. She is a friend of the Professor's wife. The skeptical Gilroy's fiancée, Agatha, is put into a trance to prove Miss Penclosa's powers. This succeeds and Gilroy begins to go to the Professor's house where Miss Penclosa practices her powers on him (one of the many things she tells him is that her powers vary with her strength). This is so Gilroy can look at the physical part of the powers.

Miss Penclosa (who has done this before) 'falls in love' with the unfortunate Gilroy. She starts to use her powers on him to make him caress and utter sweet nothings to her. He loses his temper, rejects her love, and she begins to play tricks on him with her powers. The series of cruel tricks ends with him in his Agatha's room carrying a small bottle of sulphuric acid. He notices that it is half-past three. He rushes to Miss Penclosa's home and demands for her presence at the door. The nurse there answers in a frightened tone that she died at half-past three.