A secret agent and his partner infiltrate a clandestine Satanic organization to solve a brutal murder and thwart a threat to Western security. Barney Sullivan, an operative tasked with investigating Communist subversion, discovers a link between political instability and a malevolent occult group following the death of a colleague. He recruits Mary Morden, a woman with a complicated history, to assist him in navigating the dangerous rituals of the sect. The narrative follows their descent into a world of blasphemy and violence, where they must maintain their cover while resisting the psychological influence of their adversaries. The story utilizes a third-person perspective to detail the tension between their mission objectives and the moral compromises required to survive the cult's inner circle.

Readers frequently highlight the book's blend of traditional espionage tropes with supernatural horror elements. Discussion often centers on the author's detailed, albeit sensationalized, portrayal of occult practices and the intense moral dilemmas faced by the protagonists. Critics note the pacing is deliberate, building tension through the slow revelation of the cult's influence on global politics. The work is often cited for its reflection of mid-twentieth-century anxieties regarding both political subversion and moral decay. Many readers appreciate the atmospheric world-building that distinguishes this title within the author's broader body of work.