A retired music-hall performer and his daughter, a clerk at the War Office, are drawn from domestic and theatrical scenes into a web of wartime intrigue after a sudden, consequential event. A Secret Service officer and an assortment of spies, deserters, and eccentric acquaintances pursue clues that include coded packages, hidden cellars, and unexpected visitors, unraveling layers of disguise and deception. Chapters alternate between backstage detail, cozy family moments, and suspenseful investigations, presenting both character-driven sketches and methodical detective work. The plot builds through revelations and confrontations that expose the spy network and recover a long-sought, high-value cache.