Christina Mordant finds her life upended when she discovers she is the vessel for a demonic entity controlled by a sinister occultist. Christina, an unsuspecting young woman, becomes the focal point of a dark ritual orchestrated by Canon Copely-Syle, a rogue priest seeking to manifest a demonic force. As she struggles against the encroaching influence of the entity within her, she must rely on the assistance of those who understand the gravity of the occult threat. The narrative utilizes a third-person perspective to shift between the idyllic setting of the French Riviera and the ominous, isolated marshes of Essex, heightening the contrast between normalcy and the supernatural. The characters operate within a world where ancient, malevolent forces are hidden just beneath the surface of modern society.

Readers frequently highlight the book as a quintessential example of mid-twentieth-century occult fiction. Discussion often centers on the author's meticulous attention to detail regarding ritualistic practices and the historical context of the supernatural. Critics note that the pacing effectively balances the slow-burn discovery of the protagonist's condition with the escalating tension of the antagonist's plans. The atmosphere is consistently praised for its ability to evoke a sense of unease through the juxtaposition of mundane life and dark, hidden agendas. Many readers appreciate the clear delineation between the forces of light and darkness, which remains a hallmark of the author's style.