Founded in London in 1963 by Mary Ann MacLean and Robert de Grimston, The Process Church of the Final Judgement emerged from a scientology-inspired psychotherapy group and quickly became a cultural phenomenon before its dramatic split in 1974. What did The Process truly believe? Their secretive nature kept many in the dark, but sociologist William Sims Bainbridge gained unprecedented access to this elusive group. As a young researcher in the late sixties, Bainbridge earned the trust of the Processians in Boston, becoming the only non-member to witness their rituals and practices firsthand. His rare and sought-after book, Satan's Power: A Deviant Psychotherapy Cult (1978), first unveiled his groundbreaking findings. Now, fifty years after the cult's decline, Bainbridge revisits and expands upon his seminal work in Lucifer's Power. This updated edition uncovers the motivations of The Process's members, reveals their intricate beliefs and rituals, and explores the cult's enduring legacy and influence. Packed with new material and never-before-seen historical photographs taken by Bainbridge during the height of The Process's popularity, this book provides a comprehensive and compelling look into the world of The Process Church of the Final Judgement.