Mysteries, with its long sub-title, the second book in Wilson’s “Occult Trilogy” (commencing with The Occult (1971) and concluding with Beyond the Occult (1988)), was published in the UK by Hodder & Stoughton in September 1978 and by G. P. Putnam’s Sons in the US shortly afterwards. The Occult, a book of over 600 pages, was Wilson’s first commissioned work and was so successful that the publishers requested a sequel. Wilson responded with a book of even greater length which, like its predecessor, was divided into three parts preceded by an Introduction.
This Introduction, “The Ladder of Selves”, contains some important insights and, indeed, was included by Wilson in The …
Stanley, Colin. "Mysteries: an investigation into the occult, the paranormal and the supernatural". The Literary Encyclopedia. First published 01 July 2011
[http://www.litencyc.com/php/sworks.php?rec=true&UID=23958, accessed 19 February 2017.]