A desperate agent arrives in England on a clandestine mission to secure coal supplies for his war-torn nation, only to find himself ensnared in a web of betrayal and violence.

D. is a former university lecturer turned intelligence operative who must navigate a hostile foreign landscape while being hunted by his own countrymen and foreign adversaries. His objective is to negotiate a contract that could alter the outcome of his country's civil war, yet he is hampered by a lack of resources and the constant threat of exposure. The narrative framework utilizes a third-person limited perspective, emphasizing the protagonist's isolation and the paranoia inherent in his profession. The world is defined by the grim, rain-slicked streets of pre-war London and the moral ambiguity of international politics.

Readers and critics frequently categorize this work as one of Greene's 'entertainments,' noting its focus on suspense and narrative momentum over purely philosophical inquiry. Discussion often centers on the protagonist's profound sense of alienation and the bleak, cynical atmosphere that permeates the urban setting. Many observers highlight the effectiveness of the plot's pacing, which mirrors the protagonist's own frantic and uncertain state of mind. The book is often praised for its ability to ground high-stakes political intrigue in the gritty, mundane realities of daily life. Ultimately, the narrative is viewed as a significant exploration of the intersection between individual morality and the impersonal machinery of international conflict.