The Parasite — Arthur Conan Doyle

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. Let me try to reason it out. This woman, by her own explanation, can dominate my nervous organism. She can project herself into my body and take command of it. She has a parasite soul; yes, she is a parasite, a monstrous parasite. She creeps into my frame as the hermit crab does into the whelk's shell. I am powerless! What can I do? I am dealing with forces of which I know nothing. And I can tell no one of my trouble. They would set me down as a madman. Certainly, if it got noised abroad, the university would say that they had no need of a devil-ridden professor. And Agatha! No, no, I must face it alone.