The Parasite. A Story

A rationalist physiologist agrees to be hypnotised by a small, plain, crippled woman from Trinidad, as an experiment - and discovers that she can put her will inside his and that he cannot get it out. Conan Doyle created Holmes while waiting for patients in an empty practice, and later gave his life to spiritualism; this 1894 novella is where the two halves of him meet, and it is genuinely frightening.