Old Diary Leaves was written after the death of H.P. Blavatsky, the famous sybil who had been Olcott's chief collaborator in the creation of the Theosophical Society, as well as their most conspicuous link to the Masters, Adepts, or to use the later-standard Theosophical jargon, Mahatmas. Olcott and Blavatsky had had some disagreements in the period between the events described in this volume and her later death, but his memories of her here are highly complimentary. She is presented as noble in intention, if flawed in character, and certainly in possession of supernatural powers, although these are employed in strange mixtures with trickery for purposes that are inscrutable often even to herself. Olcott suggests that he and Blavatsky's other close associates at the time may have had their perceptions routinely altered by post-hypnotic suggestions of her devising.
Olcott discusses the manner in which H.P.B. served as a vehicle for a variety of adepts who were understood to have guided the creation of the Theosophical Society and the authoring of Isis Unveiled, that erratic compendium of lore that was such a touchstone for the occultism of its era. It is important to note that Blavatsky did not profess herself, nor was she viewed by Olcott as, a passive trance medium for spirits of the dead after the fashion of the Spiritualism of the time. Spiritualism had provided the setting for these two to encounter each other initially, but their own later Theosophical occultist reading of Spiritualist phenomena held such operations to be misunderstood and misrepresented by their advocates. The "spirit controls" were actually "elemental and elementary" spirits being given undeserved free rein among human dupes. Blavatsky's possession by her Masters was in contrast a conscious collaboration with still-living humans of supernatural puissance.
In a somewhat tentative passage, that is still one of the most striking in the book, Olcott goes so far as to hypothesize that the woman Helena Blavatsky may have actually died a violent death in Europe before he met her, and that during the entire period of their association, she was animated by the combined efforts of a group of adepts who were using her as their worldly instrument.
Not all of the book is about H.P.B., however. The essential narrative is that of the creation of the Theosophical Society, from its initial combinations of Spiritualist and occultist milieux and eventual addition of Eastern (i.e. south Asian) philosophies, up until the establishment of the British branch of the Society and the departure of Olcott and H.P.B. from New York to found the new headquarters in India. A full chapter gives an accounting of the "first cremation in America," as engineered by the founding Theosophists. And there is a great deal of anecdote and description regarding the New York apartment "Lamasery" where H.P.B. wrote Isis Unveiled, and where Olcott presided over their "little Bohemia" of Victorian esotericism. Also, Olcott discusses his own experiences of astral projection, encounters with adepts, and other phenomena from which he exempts H.P.B. as an actor.
There is just no getting around the Theosophical Society in the history of modern esoteric movements, and this firsthand account of its origins is both entertaining and revealing.