Professor Challenger, The Land of Mist.
Saddly, Sir Arthur Conan Doyle did not heed the advice of his own creation. As a piece of propaganda for his personal belief in Spiritualism, Conan Doyle's The Land of Mist naturally makes many scientifically spurious claims. Of course, as a work of fiction, the author benifits from being able to control the situations his characters get into and the information presented to the reader: not only is Spiritualism true in his book, but he crafts claims which cannot be tested, such as the "behind closed doors" discussions of mediums. However, Conan Doyle does provide some textbook cases of so-called psychical phenomenon which only the artifice of fiction can allow him to present as anything but deception. This article will provide links to various articles across cyberspace that provide explanations for said phenomenon.
The story all told presents a "believer's eye view" of the Spiritualist movement in the mid-1920s. Therefore, our natural first stop will be a discussion of the history of the Spiritualist church, provided by The Story of Spiritualism. In this particular case, I am drawing from the site of a Spiritualist church, allowing them to be the source for historical information about their own religion.
The heart of Spiritualism, and therefore of The Land of Mist, is of course psychics and mediums. These vary from the stage acts of chapter 2 to the exotic and elaborate seances and mediums of chapters 4, 5, 10, and 16. At the heart of the psychic/medium routine (while psychics and mediums claim to be doing different things - reading minds and communicating with the dead respectively - their methodology is the same) is "cold" and "hot" reading. These methods have proven so durable that they are still in use today by popular mediums like John Edwards and Sylvia Browne. Several websites have ample information on these techniques: The Art of "Cold Reading" from the James Randi Educational Foundation, How to be a Psychic, and Cold Reading: Tricks of the Psychics. Speaking of John Edwards, television medium host of Crossing Over, CSICOP has provided an excellent investigative report entitled Hustling the Bereaved.
A good general overview of the subject of communicating with the dead can be found at The New Paranatural Paradigm
In chapter 13, the skeptical Professor Challenger becomes unwittingly defeated in a debate on psychical phenomenon. Naturally, the picture The Land of Mist paints is not one in favour of the skeptics, but real life debates with proponents of the paranormal place the trickery on the side of the proponents. A case in point is James Randi's ongoing debacle with Sylvia Browne, as chronicled here.
Chapter 12 treats the reader to a scene of paranormal investigation, featuring a character based loosely on psychic researcher Gustave Geley. Unfortunately, what is presented is well outside of considered methods for scientific investigation. How To Study Weird Things is a good starter on the subject, which is also covered in the above standing agreement between Browne and Randi.
Alternative medicine and faith healing is dealt with in chapter 14. The placebo effect is alive and well in those who inexplicably do not trust proven medical science. Quackwatch has extensive resources on the subject of alternative medicine.
It is hard to say what Conan Doyle would have thought of the New Age movement of today. Though the Spiritualist church proper has discipated, it's apparatus of psychics, mediums, seances, alternative medicine, pseudo-science and ghosts still remains. But one sympathetic chord a reader may find in The Land of Mist is a sincerity about morality, the afterlife, and the Ultimate Reality... A sincerity lacking in the modern New Age movement, which endures as an expression of consumerism, obsessed as it is with "personal wellness". Pop a pill to make your soul feel better. Commentary about this can be found at New Age Beliefs and Narcissism and Consumerism to Blame for Rise in Cults.
Of course, the best prevention is to get into the habit of questioning. A Field Guide to Critical Thinking is a good introduction to this necessary practice.