When an unexpected visitor arrives at the home of Department Z agent Bob Kerr, he is thrust into a lethal conspiracy originating from the principality of Vallena. Kerr seeks a quiet afternoon of respite, but his plans are thwarted by an urgent briefing regarding a series of political assassinations. The narrative follows Kerr as he navigates the immediate threat posed by a mysterious informant and the broader danger to British officials. The story utilizes a third-person perspective to track the movements of Department Z as they attempt to dismantle a clandestine criminal network before more lives are extinguished.

Readers frequently highlight the brisk pacing and the procedural focus that characterizes John Creasey's Department Z series. Discussion often centers on the author's ability to weave international intrigue into a compact, suspenseful narrative structure. Critics note that the work prioritizes plot momentum and the mechanics of espionage over deep psychological character studies. The atmosphere is often described as classic mid-century thriller writing, appealing to those who enjoy traditional detective and spy fiction. Readers appreciate how the story maintains a consistent level of tension from the initial encounter to the final resolution of the criminal threat.