In the early twentieth century, Arthur Conan Doyle and Harry Houdini were two of the most fêted and famous men alive. Their relationship was extraordinary: Arthur Conan Doyle, the creator of the ultra-rational detective Sherlock Holmes, was a believer in Spiritualism. He came to his belief that one could communicate with the dead, after his son and younger brother were killed in the First World War. He became an expert in the Spiritualist field and developed an unshakeable faith that the gap between life and death could be bridged. Harry Houdini, the world's foremost magician, was a friend of Conan Doyle's but was sceptical of his belief in the supernatural. Houdini, showman and master of mystery, took every opportunity to use his knowledge of illusion to expose psychics, and was incensed in particular by what he regarded as their exploitation of the 'nervous derangement' of grief. Drawing on previously unpublished archive material, this sensational history of two popular geniuses conjures up the early Twentieth Century and the fame, personalities and competing beliefs that pulled them apart.