The Duke de Richleau must confront an enemy utilizing occult forces to compromise Allied Atlantic convoy routes during the Second World War. Tasked with uncovering the source of German intelligence regarding secret naval paths, the Duke de Richleau discovers that the threat transcends conventional espionage. He must navigate a reality where physical warfare intersects with the metaphysical, requiring him to engage adversaries on the Astral Plane. The narrative follows his efforts to counter these supernatural incursions while maintaining the secrecy required by his wartime mission. The story utilizes a third-person perspective to detail the Duke's strategic maneuvers against both human and ethereal opponents.

Readers frequently highlight the unique blend of traditional espionage tropes and supernatural elements that define this work. Discussion often centers on the Duke de Richleau's characterization as a quintessential gentleman adventurer capable of navigating complex moral landscapes. Critics note the author's ability to maintain narrative momentum despite the transition into more fantastic territory. The balance between the grounded reality of the Atlantic convoys and the abstract nature of the Astral Plane remains a frequent point of analysis for those interested in mid-century genre fiction. The work is often cited as a distinct example of how thriller writers of the era incorporated occultism into their plots.