Arthur Conan Doyle embraced spiritualism around the end of World War I. This set of beliefs centers upon the idea that the spirits of the deceased linger and endeavor to contact the world of the living. Mediums are necessary to hold séances and allow the dead and the living to communicate. Other important aspects of spiritualism include the fact that the soul continues to live after the physical body dies, that the soul can learn and improve even after death, and that the natural world bespeaks the presence of a God, or an "Infinite Intelligence." Many believed that spirits live on a higher, third plane and can thus proffer knowledge and advice on moral, ethical, and religious issues.
Spiritualism developed and peaked in the 1840s-1920s; most of its adherents were upper or middle class citizens of English-speaking countries. Women flocked to the movement in greater numbers than men. There were few official canonical texts or formal organizations when the movement began. Most communication between members and publication of theories and activities was done through newspapers and other periodicals, camp meetings, and traveling mediums. Spiritualism lost credibility and respectability in the 1880s when reports of fraud appeared and formal organizations began to spring up. Modern spiritualism differs from late 19th and early 20th century spiritualism.
Doyle officially converted to spiritualism in 1916 along with his wife Jean. He joined the Ghost Club, an organization founded in 1862 to investigate and research paranormal activities such as ghosts and hauntings. Other famous members included, at one point or another, Charles Dickens, W.B. Yeats, and Sir William Crookes. In 1917 two young girls, Francis Griffiths and Elsie Wright, displayed photographs that they claimed were of fairies in their garden. Many were completely convinced that the photos of the Cottingley Fairies, as they came to be called, were genuine. This group included Doyle, who even defended the verisimilitude of the photos in pamphlets and a book. This led to public criticism of Doyle, most celebrated for his rational and reasonable Sherlock Holmes.
Some of Doyle's works dealt with spiritualist concerns. In his work, The Edge of the Unknown, he spent a chapter arguing that Houdini had legitimate psychic power but never revealed it.
Many of Doyle's supporters and biographers have had difficulty coming to terms with his embrace of such a uncommon set of religious beliefs. Nevertheless, most readers of the famed Sherlock Holmes stories are either unaware of their creator's odd beliefs, or find this fact irrelevant to his creation of one of the most brilliant and enigmatic characters in literature.