Cosmic Trigger I: The Final Secret of the Illuminati

Part memoir, part epistemological experiment: Wilson deliberately induced belief in a series of increasingly strange models — Sirius transmissions, magick, the 23 enigma — and reports honestly on what happened, including the death of his daughter in the middle of it.

The book where Chapel Perilous is named. It is also the most emotionally serious thing he wrote, and the best argument for holding models loosely.