An ostensibly ordinary man becomes entangled in international intrigue and must flee to survive after learning of a conspiracy. The setup focuses on pursuit, mistaken identity (or forced suspicion), and a race to uncover key information before hostile agents can stop him.

Set in late-19th-century London, the novel follows an agent involved in espionage for an unnamed foreign power amid a small circle touched by anarchist agitation. The book traces the effects of political plotting and covert operations on ordinary lives, especially relationships marked by dependency and vulnerability.