American professor John Holden arrives in London for a conference on parapsychology only to discover that the colleague he was supposed to meet was killed in a freak accident the day before. It turns out that the deceased had been investigating a cult lead by Dr. Julian Karswell. Though a skeptic, Holden is suspicious of the devil-worshiping Karswell. Following a trail of mysterious manuscripts, Holden enters a world that makes him question his faith in science.

An American army officer working for British intelligence comes to post-war Berlin to solve a murder. His investigation is compromised when he falls for a nightclub singer, not realising she is an agent of the criminal mastermind he is on the trail of.