The spirit was said to have appeared first in 1871 in séances conducted by Florence Cook in London, and later in 1874-1875 in New York in séances held by the mediums Jennie Holmes and her husband Nelson Holmes.
Katie King was believed by Spiritualists to be the daughter of John King, a spirit control of the 1850s through the 1870s that appeared in many séances involving materialized spirits. A spirit control is a powerful and communicative spirit that organizes the appearance of other spirits at a séance. John King claimed to be the spirit of Henry Morgan, the buccaneer (Doyle 1926: volume 1, 241, 277).
Between 1871 and 1874, Sir William Crookes, investigated the preternatural phenomena produced by Spiritualist mediums. He described the conditions he imposed on mediums as follows: "It must be at my own house, and my own selection of friends and spectators, under my own conditions, and I may do whatever I like as regards apparatus" (Doyle 1926: volume 1, 177).
At Hackney in 1863, lawyer William Volckman attended a séance held by Florence Cook, during which Katie King materialized. Suspicious of the spirit's similarity with Cook, Volckman seized the spirit, accusing it of being the medium masquerading as her ghost. Considered an exposure by Volckman and his allies, supporters of Miss Cook denounced Volckman's act on the grounds that he had broken his agreement to proper etiquette required in the séance, thus negating his credibility as an investigator. Moreover it was argued that since spirits borrowed energy and matter from their medium, it was not surprising that Katie King resembled Cook. Despite the defense of their position, Cook and her supporters were hurt by this incident, and sought greater evidence to support their position. To this endeavour, they turned to Crookes, who was a prominent and respected scientist (Noakes, 130-1).
A 15 year old Cook, alone in Crookes' house with Crookes' friends and family as witnesses, was said to have materialized the spirit of Katie King, who walked about, talked, allowed herself to be weighed and measured, and even held the family's baby (Doyle 1926: volume 1, 241). The sessions were held in the dark, because Spiritualists believe that materialization requires very dim surroundings to succeed, though occasionally some red light was used and some photographs were taken. As is apparently typical of materialized spirits, Katie's exact height and weight varied, though Katie was always taller than Florence Cook, with a larger face, and different hair and skin. According to those present, the two were both visible at the same moments, so that Florence could not have assumed the role of the spirit (Doyle 1926: volume 1, 235-240).
Crookes' report, published in 1874, contained his assertion that Florence Cook, as well as the mediums Kate Fox and Daniel Dunglas Home, were producing genuine preternatural phenomena (Crookes 1874). The publication caused an uproar, and his testimony about Katie King was considered the most outrageous and sensational part of the report. Crookes very nearly lost his Fellowship at the Royal Society, and did not again engage in Spiritualist research (Doyle 1926: volume 1, 169).
Just as the article was going to press, however, a woman named Eliza White stepped forward and claimed to have masqueraded as Katie. White's face matched that of "Katie King" in photographs sold by the Holmeses and their agents. Both the Atlantic Monthly and Owen admitted in public to being duped. Arthur Conan Doyle maintains that this "exposure" did more damage to Spiritualism than any other exposure of the period (Doyle 1926: volume 1, 269-277).
Investigations conducted by leading Spiritualist Henry Steel Olcott in 1875 re-established the credibility of the Holmeses in the eyes of many Spiritualists. The story eventually accepted by most Spiritualists was that Eliza White had been hired to pose as Katie King for a photograph to sell to the public. The Holmeses had not wanted to photograph the real Katie King, since bright light would have ruined the materialization. Once involved, Eliza White first extorted money from the Holmeses, and then sold the story to the press (Doyle 1926: volume 1, 269-277).