After being targeted by foreign agents for his work on a Turkish naval project, an ordinary engineer finds himself trapped on a steamer ship with no way to identify his assassins. Graham, a man defined by his professional expertise rather than his combat skills, must navigate a claustrophobic environment where every passenger is a potential threat. His objective is to survive the voyage back to England while his adversaries employ psychological and physical tactics to ensure he never reaches his destination. The narrative utilizes a third-person perspective to emphasize Graham's growing isolation and the mounting paranoia inherent in his predicament.

This work is widely regarded as a foundational text in the development of the modern espionage thriller. Critics frequently highlight Ambler's ability to transform an ordinary civilian into a compelling protagonist who lacks the typical heroic tropes of the genre. The narrative is often praised for its clinical, detached prose style which effectively mirrors the cold calculations of the intelligence agents pursuing the protagonist. Readers often note that the book maintains a high level of tension despite its relatively modest scale and lack of explosive set pieces. The story remains a standard for those interested in the evolution of suspense literature during the mid-twentieth century.