American professor John Holden travels to London for a parapsychology conference, only to learn that his colleague was killed in a bizarre accident just prior. Delving into the circumstances surrounding the death, he uncovers a sinister cult led by Dr. Julian Karswell. Despite his skeptical nature, Holden grows increasingly uneasy about Karswell's devil-worship practices. As he follows a series of enigmatic manuscripts, he is drawn into a realm that challenges his staunch belief in science, forcing him to confront the very real possibility of supernatural forces at play.