Jaher's book focuses not so much on the growth of spiritualism as a movement so much as Harry Houdini's long-running feud with spiritualist mediums and his efforts to expose them as frauds. Specifically the book focuses on Harry Houdini and Mina Crandon, a Boston socialite who was for a period of time considered to be the best example of the legitimate thing. As Jaher argues, Crandon's social status, as well as the fact she did not perform seances for money, may have contributed to the long period of belief people had in her abilities, however Houdini did not believe her from the start and eventually other individuals declared her a fraud as well, although Crandon never admitted so during her life.
There are a couple of reasons for this enmity. First in earlier points of his career Houdini actually performed as a medium in various travelling shows so he was well aware of the various tricks utilized by mediums to gain the confidence of their audience. Second, Houdini was part of a commission made by the magazine Popular Science to investigate into whether any claims made by mediums of supernatural or supernormal abilities had any merit, with a considerable cash prize for any confirmed psychics. Including several scientists, Houdini and the committee revealed several frauds, including Mrs. Crandon, before Popular Science abandoned the search for a genuine psychic. When many other people seemed to be taken in by Mrs. Crandon's performances, Houdini remained unconvinced and one of the most outspoken critics of mediums and spiritualism, gaining the ire of the spiritualist community.
I do find the phenomenon of spiritualism to be understandable, if incredibly suspicious from the beginning. After all, people who were separated from family members early in their life or in the prime of their life would have a strong desire to connect with their loved ones and know that they were okay after death. However from the beginning the amazing feats of mediums happened in very suspicious circumstances. For example, seances were only undertaken in darkness or extremely dim light because the spirits and ectoplasm did not like bright light. So mysterious levitations could be barely seen or couldn't be seen at all, making the opportunity for all sorts of trickery possible. In addition, mediums often put themselves in spirit cabinets, an area where they were secluded and often obscured from sight and from which they'd work miracles. Even to some contemporaries all this behavior seemed highly suspicious and unsurprisingly when placed in controlled conditions the mediums were unable to produce many of their miraculous effects. Of course this seldom discouraged the strongest believers in spiritualism or the mediums, merely stating that the hostile mood of the circle or some other thing was responsible for the failure of the spirits.
Overall this book is an interesting look at a subculture of American life during the 1920's. However, it is fairly specific in its focus and may not be terribly interesting to people who don't wish to study spiritualism. If you're curious about the movement and the various ways in which mediums engaged in trickery during this time period it's well worth looking at, but otherwise I think you can safely pass this by.